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In the diatom Phaeodactylum tricornutum, iron limitation promotes a decrease in the content of photosystem II, as determined by measurements of oxygen-evolving activity, thermoluminescence, chlorophyll fluorescence analyses and protein quantification methods. Thermoluminescence experiments also indicate that iron limitation induces subtle changes in the energetics of the recombination reaction between reduced QB and the S2/S3 states of the water-splitting machinery. However, electron transfer from QA to QB, involving non-heme iron, seems not to be significantly inhibited. Moreover, iron deficiency promotes a severe decrease in the content of the extrinsic PsbV/cytochrome c550 subunit of photosystem II, which appears in eukaryotic algae from the red photosynthetic lineage (including diatoms) but is absent in green algae and plants. The decline in the content of cytochrome c550 under iron-limiting conditions is accompanied by a decrease in the binding of this protein to photosystem II, and also of the extrinsic PsbO subunit. We propose that the lack of cytochrome c550, induced by iron deficiency, specifically affects the binding of other extrinsic subunits of photosystem II, as previously described in cyanobacterial PsbV mutants. Ministerio de Economía y Competitividad BIO2015-64169-P Universidad de Sevilla US-1380339

Objetivos: medir la prevalencia e intensidad del dolor agudo en pacientes hospitalizados en el Servicio de Neurocirugía de un Hospital Terciario, utilizando una escala verbal numérica, la Escala Visual Analógica (EVA) para su evaluación. Material y métodos: estudio observacional, transversal, para evaluar el dolor agudo. Se incluyen todos los pacientes ingresados en planta durante noviembre del 2019 y se excluyen aquellos con limitaciones para entender o evaluar el dolor según EVA. Resultados: del total de 120 pacientes ingresados en planta durante el periodo de estudio, son excluidos 40 por no cumplir los criterios de inclusión. Se analizan 80 pacientes que presentan elevada prevalencia de dolor (76,61%), con una puntuación media de 3,47 ± 0.78. De los que refieren dolor, en un 20% es leve, 40% moderado y 40% intenso. Por patologías los valores más elevados corresponden a post-intervención. Los protocolos analgésicos del Hospital se aplicaron en todos los casos y ningún paciente acudió a urgencias por dolor tras el alta hospitalaria. La principal limitación del estudio fue que no en todos los pacientes se recogió adecuadamente la puntuación EVA. Conclusiones: la prevalencia de dolor en una planta de neurocirugía es elevada (76,61%), con unas puntuaciones medias (3-4, dolor moderado) que requieren mejorar nuestras estrategias analgésicas y la medición del mismo. Las enfermedades malignas, de predominio intracraneal, se asociaron con mayor dolor.

Background: The incidence of vertebral fractures is high and the new treatment options developed in recent years represent a significant improvement, although they are not without complications. Objectives: The aim of this study was to investigate whether percutaneous vertebral augmentation (PVA) was associated with clinical and radiological subsequent adjacent fractures. Methods: A systematic review and meta-analysis was performed searching on PubMed, EMBASE, Cochrane library, Google Scholar, Web of Science, and ClinicalTrial.gov from the establishment of the database to January 2020. Eligible studies assessing the subsequent adjacent fractures after PVA compared with conservative treatment (CT) were incorporated. The pooled risk ratio (RR) with its 95% confidence intervals (95% CI) was used. Heterogeneity, sensitivity, and publication bias analyses were performed. Results: Twenty-four studies were considered eligible and were included finally. 20/421 patients (4.75%) had clinical subsequent adjacent fractures from the PVA group, and 25/359 patients (6.96%) had from the CT group, and 46/440 patients (10.45%) from the PVA group and 36/444 patients (8.10%) from the CT group had radiological subsequent adjacent fractures. There both had no significant difference between two groups (RR = 0.67, 95%CI: [0.38, 1.19], p = 0.17)/(RR = 1.13, 95% CI: [0.75, 1.70], p = 0.576). However, in fractured vertebrae, number in the PVA group was more than that in the CT group (RR=1.41, 95%CI: [1.03, 1.93], p = 0.03). Conclusion: Collectively, currently available literature provides data showed that PVA did not increase the incidence for subsequent adjacent fractures, no matter it was clinical or radiological fracture. However, PVA may increase the number of fractured vertebrae. Antecedentes: La incidencia de fracturas vertebrales es elevada y las nuevas opciones de tratamiento desarrolladas en los últimos años suponen una mejoría importante, aunque no se encuentran exentas de complicaciones. Objetivos: El objetivo de este estudio fue investigar si el tratamiento vertebral percutáneo se asoció con fracturas en los niveles adyacentes, tanto clínicas como radiológicas, en los controles posteriores. Métodos: Se realizó una revisión sistemática y un metanálisis buscando en PubMed, EMBASE, la biblioteca Cochrane, Google Scholar, Web of Science y ClinicalTrial.gov desde el establecimiento de la base de datos hasta enero de 2020. Se eligieron estudios elegibles que evalúan las fracturas adyacentes posteriores después de PVA en comparación con tratamiento conservador (CT). Se utilizó la razón de riesgo (RR), agrupada con sus intervalos de confianza del 95% (IC del 95%). Se realizaron análisis de heterogeneidad, de sensibilidad y de sesgo de publicación. Resultados: Se consideraron elegibles 24 estudio, que se incluyeron finalmente. Del total de pacientes estudiados, 20/421 pacientes (4.75%) tuvieron fracturas adyacentes clínicas posteriores del grupo PVA, y 25/359 pacientes (6,96%) tuvieron del grupo CT, y 46/440 pacientes (10.45%) del grupo PVA y 36/444 pacientes (8.10 %) del grupo CT tenía fracturas adyacentes radiológicas posteriores. No existieron diferencias significativas entre los dos grupos (RR = 0.67, IC 95%: [0.38, 1.19], p = 0.17) / (RR = 1.13, IC 95%: [0.75, 1.70], p = 0.576). Sin embargo, en las vértebras fracturadas, el número en el grupo PVA fue mayor que en el grupo CT (RR = 1.41, IC 95%: [1.03, 1.93], p = 0.03). Conclusión: Desde un punto de vista general, la literatura actualmente disponible proporciona datos que muestran que el PVA no aumentó la incidencia de fracturas adyacentes posteriores, sin importar si fue una fractura clínica o radiológica. Pero el PVA puede aumentar el número de vértebras fracturadas.

Electric motors are valuable, long-life industrial assets, whose lifespan is often measured in decades. A period of unplanned motor downtime in an industrial plant frequently incurs an expenditure of thousands of euros per hour. As a consequence, plant engineers often focus their decisions on reliability rather than on operating cost (energy bill). Unfortunately, the high price of energy and its growing trend mean that operating cost has an increasingly negative impact on production cost and company competitiveness. The problem of selecting the rated power of a line-operated single-speed electric motor to drive a time-variable mechanical load has traditionally been solved, based on the well-established root mean square (RMS) value of the time-power profile of the mechanical load. This conventional method of rating is strictly technical, since the rated power of the motor is determined, based only on the power profile of the load. No other factors are considered, such as the energy consumption throughout the whole in-service life of the motor, or, even better, the whole life cycle cost (LCC), which is defined as the net present value of purchasing, installing, operating (energy), maintaining and decommissioning the motor throughout its life. As a consequence, conventional rating often leads to the selection of motors with a power rating that is technically sufficient to drive the mechanical load, but insufficient to do so with the lowest possible energy (losses) consumption, or even better, with the lowest possible life cycle cost. A new analytical method to determine the techno-economic optimum power rating of a line-operated single-speed electric motor to drive a time-variable mechanical load will be introduced in this paper. The proposed method takes into account not only the technical restrictions due to the time-power profile of the mechanical load, but also the whole life cycle cost. Based on the list of electric motors offered in the manufacturer’s catalogue, the new methodology enables the optimum techno-economic rated power of the motor to be calculated, which minimizes the energy consumption (energy loss) throughout its in-service life or its total life cycle cost. The results show that the optimum techno-economic rating is one or two rated-power levels above the conventional rating based solely on the RMS load.

\ₑprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/ppl.13323

We have investigated if the heterologous expression of a functional green alga plastocyanin in the diatom Phaeodactylum tricornutum can improve photosynthetic activity and cell growth. Previous in vitro assays showed that a single-mutant of the plastocyanin from the green algae Chlamydomonas reinhardtii is effective in reducing P. tricornutum photosystem I. In this study, in vivo assays with P. tricornutum strains expressing this plastocyanin indicate that even the relatively low intracellular concentrations of holo-plastocyanin detected (≈4 μM) are enough to promote an increased growth (up to 60%) under iron-deficient conditions as compared with the WT strain, measured as higher cell densities, content in pigments and active photosystem I, global photosynthetic rates per cell, and even cell volume. In addition, the presence of plastocyanin as an additional photosynthetic electron carrier seems to decrease the over-reduction of the plastoquinone pool. Consequently, it promotes an improvement in the maximum quantum yield of both photosystem II and I, together with a decrease in the acceptor side photoinhibition of photosystem II—also associated to a reduced oxidative stress—a decrease in the peroxidation of membrane lipids in the choroplast, and a lower degree of limitation on the donor side of photosystem I. Thus the heterologous plastocyanin appears to act as a functional electron carrier, alternative to the native cytochrome c6, under iron-limiting conditions. Junta de Andalucía PAIDI BIO-022 Ministerio de Economía y Competitividad BIO2015-64169-P

The photosynthetic cytochrome c550 from the marine diatom Phaeodactylum tricornutum has been purified and characterized. Cytochrome c550 is mostly obtained from the soluble cell extract in relatively large amounts. In addition, the protein appeared to be truncated in the last hydrophobic residues of the C-terminus, both in the soluble cytochrome c550 and in the protein extracted from the membrane fraction, as deduced by mass spectrometry analysis and the comparison with the gene sequence. Interestingly, it has been described that the C-terminus of cytochrome c550 forms a hydrophobic finger involved in the interaction with photosystem II in cyanobacteria. Cytochrome c550 was almost absent in solubilized photosystem II complex samples, in contrast with the PsbO and Psb31 extrinsic subunits, thus suggesting a lower affinity of cytochrome c550 for the photosystem II complex. Under iron-limiting conditions the amount of cytochrome c550 decreases up to about 45% as compared to iron-replete cells, pointing to an iron-regulated synthesis. Oxidized cytochrome c550 has been characterized using continuous wave EPR and pulse techniques, including HYSCORE, and the obtained results have been interpreted in terms of the electrostatic charge distribution in the surroundings of the heme centre., This work was supported by the Spanish Ministry of Economy and Competitiveness (BIO2012-35271, BIO2015-64169-P, MAT2011-23861 and CTQ2015-64486-R) the Andalusian Government (PAIDI BIO-022) and the Aragón Government (Grupo consolidado B-18). All these grants were partially financed by the EU FEDER Program

The afterglow (AG) luminescence is a delayed chlorophyll fluorescence emitted by the photosystem II that seems to reflect the level of assimilatory potential (NADPH+ATP) in chloroplast. In this work, the thermoluminescence (TL) emissions corresponding to the AG band were investigated in plants of the WT and the Ljgln2-2 photorespiratory mutant from Lotus japonicus grown under either photorespiratory (air) or non-photorespiratory (high concentration of CO2) conditions. TL glow curves obtained after two flashes induced the strongest overall TL emissions, which could be decomposed in two components: B band (tmax =27–29∘C) and AG band (tmax =44–45∘C). Under photorespiratory conditions, WT plants showed a ratio of 1.17 between the intensity of the AG and B bands (IAG/IB). This ratio increased considerably under non-photorespiratory conditions (2.12). In contrast, mutant Ljgln2-2 plants grown under both conditions showed a high IAG/IB ratio, similar to that of WT plants grown under non-photorespiratory conditions. In addition, high temperature thermoluminescence (HTL) emissions associated to lipid peroxidation were also recorded. WT and Ljgln2-2 mutant plants grown under photorespiratory conditions showed both a significant HTL band, which increased significantly under non-photorespiratory conditions. The results of this work indicate that changes in the amplitude of IAG/IB ratio could be used as an in vivo indicator of alteration in the level of photorespiratory metabolism in L. japonicus chloroplasts. Moreover, the HTL results suggest that photorespiration plays some role in the protection of the chloroplast against lipid peroxidation.

© 2014. Thermoluminescence is a simple technique very useful for studying electron transfer reactions on photosystem II (standard thermoluminescence) or the level of lipid peroxidation in membranes (high temperature thermoluminescence) in photosynthetic organisms. Both techniques were used to investigate the effects produced on Chlorella vulgaris cells by six compounds: the chemical intermediates bromobenzene and diethanolamine, the antioxidant propyl gallate, the semiconductor indium nitrate, the pesticide sodium monofluoroacetate and the antimalarial drug chloroquine. Electron transfer activity of the photosystem II significantly decreased after the exposure of Chlorella cells to all the six chemicals used. Lipid peroxidation was slightly decreased by the antioxidant propyl gallate, not changed by indium nitrate and very potently stimulated by diethanolamine, chloroquine, sodium monofluoroacetate and bromobenzene. For five of the chemicals studied (not bromobenzene) there is a very good correlation between the cytotoxic effects in Chlorella cells measured by the algal growth inhibition test, and the inhibition of photosystem II activity. The results suggest that one very important effect of these chemicals in Chlorella cells is the inhibition of photosynthetic metabolism by the blocking of photosystem II functionality. In the case of sodium monofluoroacetate, diethanolamine and chloroquine this inhibition seems to be related with the induction of high level of lipid peroxidation in cells that may alter the stability of photosystem II. The results obtained by both techniques supply information that can be used as a supplement to the growth inhibition test and allows a more complete assessment of the effects of a chemical in photosynthetic organisms of aquatic ecosystems.

The photosynthetic cytochrome c

Iron limitation is the major factor controlling phytoplankton growth in vast regions of the contemporary oceans. In this study, a combination of thermoluminescence (TL), chlorophyll fluorescence, and P700 absorbance measurements have been used to elucidate the effects of iron deficiency in the photosynthetic electron transport of the marine diatom P. tricornutum. TL was used to determine the effects of iron deficiency on photosystem II (PSII) activity. Excitation of iron-replete P. tricornutum cells with single turn-over flashes induced the appearance of TL glow curves with two components with different peaks of temperature and contributions to the total signal intensity: the B band (23 C, 63%), and the AG band (40 C, 37%). Iron limitation did not significantly alter these bands, but induced a decrease of the total TL signal. Far red excitation did not increase the amount of the AG band in iron-limited cells, as observed for iron-replete cells. The effect of iron deficiency on the photosystem I (PSI) activity was also examined by measuring the changes in P700 redox state during illumination. The electron donation to PSI was substantially reduced in iron-deficient cells. This could be related with the important decline on cytochrome c6 content observed in these cells. Iron deficiency also induced a marked increase in light sensitivity in P. tricornutum cells. A drastic increase in the level of peroxidation of chloroplast lipids was detected in iron-deficient cells even when grown under standard conditions at low light intensity. Illumination with a light intensity of 300 mE m2 s1 during different time periods caused a dramatic disappearance in TL signal in cells grown under low iron concentration, this treatment not affecting to the signal in iron-replete cells. The results of this work suggest that iron deficiency induces partial blocking of the electron transfer between PSII and PSI, due to a lower concentration of the electron donor cytochrome c6. This decreased electron transfer may induce the over-reduction of the plastoquinone pool and consequently the appearance of acceptor side photoinhibition in PSII even at low light intensities. The functionality of chlororespiratory electron transfer pathway under iron restricted conditions is also discussed

he characteristic features of two types of short-term light adaptations of the photosynthetic apparatus of the cyanobacterium Synechocystis sp. PCC 6803, state transition and blue-green light-induced fluorescence quenching, were compared in wild-type and cytochrome b559 and PsbJ mutant cells with mutations on and near the QC site in photosystem II (PSII). All mutant cells grew photoautotrophically and assembled stable PSII. Thermoluminescence emission experiments showed a decrease in the stability of the S3QB–/S2QB– charge pairs in the A16FJ, S28Aβ, and V32Fβ mutant cells. When dark-adapted wild-type and mutant cells were illuminated by medium-intensity blue light, the increase in the PSII fluorescence yield (indicating a transition to state 1) was more prominent in mutant than wild-type cells. Strong blue-light conditions induced a quenching of fluorescence corresponding to nonphotochemical fluorescence quenching (NPQ). The extension of NPQ decreased significantly in the mutants, and the kinetics appeared to be affected. When similar measures were repeated on an orange carotenoid protein (OCP)-deficient background, little or no quenching was observed, which confirms that the decrease in fluorescence under strong blue light corresponded to the OCP-dependent NPQ. Immunoblot results showed that the attenuated effect of blue light-induced NPQ in mutant cells was not due to a lack of OCP. Photosynthetic growth and biomass production were greater for A16FJ, S28Aβ, and V32Fβ mutant cells than for wild-type cells under normal growth conditions. Our results suggest that mutations of cytochrome b559 and PsbJ on and near the QC site of PSII may modulate the short-term light response in cyanobacteria.

Resumen Introduccion El papiloma atipico de plexos coroideos es un tumor infrecuente, recientemente reconocido por la Organizacion Mundial de la Salud, con muy pocos casos publicados hasta la fecha. Los tumores de plexos coroideos son neoplasias intraventriculares raras que derivan del epitelio de los plexos coroideos, siendo los papilomas mucho mas frecuentes que los carcinomas. La gran mayoria se localiza, en la edad pediatrica, a nivel de los ventriculos laterales; los del IV ventriculo son mas frecuentes en adultos. La cirugia es curativa en los papilomas, con un porcentaje de supervivencia de casi el 100% a los 5 anos y recurrencias ocasionales. En los carcinomas la cirugia radical es dificil, es necesario un tratamiento adyuvante y el pronostico es peor, con baja supervivencia a los 5 anos. Presentamos un caso de papiloma atipico de plexos coroideos en el adulto, localizado en el IV ventriculo, sobre el que se discuten las opciones terapeuticas, a la vez que se realiza una revision de la bibliografia publicada. Caso clinico Paciente varon de 38 anos con papiloma atipico de plexos coroideos en el adulto localizado en el IV ventriculo, extirpado en su totalidad mediante craniectomia de fosa posterior y tratamiento telovelar. Conclusion El papiloma atipico de plexos coroideos por definicion tiene un riesgo mayor de recidiva o transformacion maligna respecto al papiloma “tipico”. Por ello, la reseccion quirurgica completa y el estrecho seguimiento son actualmente el tratamiento mas fiable. Sin embargo, la quimioterapia y la radioterapia postoperatorias deberian considerarse en casos de extirpacion parcial, recidiva o diseminacion.

Resumen Introduccion En la literatura se recogen alrededor de 600 casos de hematomas epidurales espinales. En varios estudios, se afirma que la incidencia de paraparesia secundaria a anestesia epidural oscila entre 0,0005–0,02%. Se han descrito numerosas etiologias, incluyendo cirugia, traumatismos, anticoagulacion, malformaciones arteriovenosas, embarazo, procesos hematologicos y puncion lumbar. Los procedimientos anestesicos raquideos y epidurales representan la decima causa mas frecuente. Pero en combinacion con el tratamiento anticoagulante, dichos procedimientos aumentan su incidencia hasta alcanzar la quinta causa. Publicamos un caso clinico de hematoma epidural cervical yatrogenico en el adulto y el buen resultado obtenido con tratamiento conservador. Caso clinico Paciente varon de 80 anos, que a las 2 horas de tratamiento analgesico de cervicoartrosis mediante infiltracion epidural cervical desarrolla intensa cervicalgia y perdida de fuerza en extremidades inferiores, mostrando paraplejia completa con arreflexia. En RM cervical se evidencia hematoma epidural entre los niveles C4 y T1. Es trasladado a nuestro centro para cirugia pero ante la rapida recuperacion se decide tratamiento medico conservador. Al mes de seguimiento, la situacion clinica es similar a la previa, sin secuelas con completa reabsorcion del hematoma en RM control. Conclusion Actualmente, la tendencia general es realizar cirugia en pacientes con hematoma espinal y empeoramiento neurologico importante durante las primeras horas. Sin embargo, se pueden obtener buenos resultados neurologicos con tratamiento conservador, en pacientes bien seleccionados con deficit parcial, incompleto y no progresivo. En el presente, no estamos en condiciones de decir que tratamiento es el mejor para cada caso concreto.

Kinetic curves of reduction of the oxidized bacteriochlorophyll dimer by the proximal heme of cytochrome in seven mutated reaction centers from Rps. viridis was measured in the temperature range of 295-10 K under an ambient potential when two high-potential hemes were reduced. The data are analyzed in frames of a model which accounts for slow medium dynamics (the diffusion-reaction equation) and the quantum effect in the modes responsible for reorganization of the cofactors and the medium. The model reproduces the observed nonexponential kinetics down to the lowest temperature where the fast kinetic component still survives. The modeling results in determination of an average characteristic time for re-orientation of dipoles of the protein matrix as a function of temperature. At temperatures above the glass-transition temperature, this function shows Arrhenius behavior with the activation energy varying between the values of 0.5 eV for wild type Rps. viridis and 0 eV for Rps. sulfoviridis found previously. Possible reasons for disappearance of the fast kinetic component in some reaction centers under study at low temperatures are discussed.

In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi–Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4–0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed. España, Ministerio de Educación y Ciencia BFU2004-04914-C02-01/BMC Junta de Andalucía PAI CVI-261

The cytochrome b559 is a heme-bridged heterodimeric protein with two subunits, α and β. Both subunits from Synechocystis sp. PCC 6803 have previously been cloned and overexpressed in Escherichia coli and in vivo reconstitution experiments have been carried out. The formation of homodimers in the bacterial membrane with endogenous heme was only observed in the case of the β-subunit (β/β) but not with the full length α-subunit. In the present work, reconstitution of a homodimer (α/α) cytochrome b559 like structure was possible using a chimeric N-terminus α-subunit truncated before the amino acid isoleucine 17, eliminating completely a short amphipathic α-helix that lays on the surface of the membrane. Overexpression and in vivo reconstitution in the bacteria was clearly demonstrated by the brownish color of the culture pellet and the use of a commercial monoclonal antibody against the fusion protein carrier, the maltoside binding protein, and polyclonal antibodies against a synthetic peptide of the α-subunit from Thermosynechococcus elongatus. Moreover, a simple partial purification after membrane solubilization with Triton X-100 confirmed that the overexpressed protein complex corresponded with the maltoside binding protein-chimeric α-subunit cytochrome b559 like structure. The features of the new structure were determined by UV–Vis, electron paramagnetic resonance and redox potentiometric techniques. Ribbon representations of all possible structures are also shown to better understand the mechanism of the cytochrome b559 maturation in the bacterial cytoplasmic membrane., This work was supported by Grants from the Spanish Ministry of Economy and Competitiveness (MINECO) (AGL2011-23574, MAT2011-23861, BIO2012-35271, BFU2010-16297), the Aragón Regional Government (E33 and B18), and the Andalucía Regional Government (PADI BIO-022). All these Grants were partially financed by the EU FEDER Program.

Electron transfer (ET) in the reaction center from Rhodopseudomonas viridis has been studied experimentally by our group in the range of temperatures of 153–295 K. The kinetics of ET reaction from the proximal heme of cytochrome to the special pair was found to be non-exponential. The degree of non-exponentiality strongly depends on temperature, with increasing non-exponentiality at lower temperatures. Here, the experimental kinetic data for ET are analyzed in the frames of a theoretical Sumi–Marcus-type model, which allows establishing a connection between the observed kinetics and local structural dynamics of the protein in a close vicinity of the donor and acceptor sites. The phenomenological model subdivides the multi-time-scale dynamics of the protein into two groups: fast and slow. The division is determined by the rate of ET, which is dynamically controlled by the slow modes of the protein medium. The slow modes are described by a phenomenological collective coordinate , for which a diffusion type ...

The afterglow (AG) band of thermoluminescence (TL) has been investigated in leaves of Arabidopsis thaliana. Excitation of dark-adapted leaves with two saturating single turn-over flashes induced the appearance of a complex TL glow curve that could be well simulated by three components: the two components, B1 and B2, of the usually called B-band, peaking at 18 and 26 degrees C, respectively, and a band with tmax at 41 degrees C, which we attributed to an AG emission. Illumination of dark-adapted leaves with 720 nm monochromatic and FR lights generated the emission of a sharp single band peaking also around at 41 degrees C, that it is usually assigned to an AG emission band. Dark-incubation of whole plants increased the intensity of AG-band in TL curves induced by two flashes and, in parallel, decreased B-bands. Selective illumination of leaves with light mostly absorbed by PS II (650 nm light) completely abolished the AG-band induced by two flashes, B-band being the only TL band observed. The single AG-band induced by 720 nm light was abolished if leaves were also illuminated with 650 nm light. On the other hand, AG-band could be restored if 650 nm illuminated leaves were afterwards illuminated with 720 nm light. The changes in the intensity of B and AG bands induced by selective illuminations seem to be related to alterations in the redox state of QB and plastoquinone pool.

The recombination reactions of Photosystem II have been investigated in vivo in rice leaves by using the thermoluminescence (TL) emission technique. Excitation of dark-adapted leaf segments at 0 °C with different number of single turn-over flashes induced the appearance of complex TL glow curves. The mathematical analysis of these curves showed the existence of four TL components: B1-band (temperature maximum, tmax, at 24 °C, originating from S3Q − recombination), B2-band (tmax at 35 °C, from S2Q − ), AG-band (tmax at 46 °C) and C-band (tmax at 55 °C, from Tyr D + Q A − ). Their contributions to the total TL signal were different depending on the number of flashes given. AG-band seems to reflect a special electron transfer from some unknown stroma donor to PS II. Q-band (tmax at 19 °C), originating from S2Q A − recombination, was recorded after flashing samples incubated in the presence of DCMU. The recombination halftimes (t1/2) at 20 °C of S2Q A − , S3Q B − , S2Q B − and Tyr D + Q A − were, respectively, 0.8 s, 48 s, 74 s and about 1 h. A sharp AG-band (tmax at 50 °C and t1/2 of 210 s) could be also observed after illumination of leaves with far-red light and after a dark incubation period of whole plants. Incubation of leaf segments with 0.5 M NaCl abolished the inductions of AG-band by darkness and far-red illumination, significantly decreased Q-band intensity, whereas induced a strong increase in C-band intensity. The possible inhibition of S2/S3 formation and quinone oxidation by saline stress are discussed.

This paper develops a weighted least-squares methodology for the estimation of relevant parameters characterizing harmonic polluting industrial loads through a set of measurements acquired at the point of common coupling. The proposed method is capable of obtaining an accurate load model in the absence of detailed information about its internal structure and composition.

This paper focuses on the steady-state response of existing methods for computing the reference current of active power filters. For each class of methods, the main source of discrepancy between the load harmonic current and the computed reference current is identified and the frequency spectrum of the resulting error is analytically determined. Although this topic has been partially addressed in previous publications, the proposed frequency-domain approach provides valuable qualitative information about how the errors are produced and distributed, which is masked when the analysis is carried out in the time domain. First, the frequency-domain formulation is separately presented for each method. Then, a comparison of the resulting errors is performed on a case study. Finally, some experimental results are given to validate the proposed frequency-domain analysis.

Cytochrome c550 is one of the extrinsic Photosystem II subunits in cyanobacteria and red algae. To study the possible role of the heme of the cytochrome c550 we constructed two mutants of Thermosynechococcus elongatus in which the residue His-92, the sixth ligand of the heme, was replaced by a Met or a Cys in order to modify the redox properties of the heme. The H92M and H92C mutations changed the midpoint redox potential of the heme in the isolated cytochrome by +125 mV and –30 mV, respectively, compared with the wild type. The binding-induced increase of the redox potential observed in the wild type and the H92C mutant was absent in the H92M mutant. Both modified cytochromes were more easily detachable from the Photosystem II compared with the wild type. The Photosystem II activity in cells was not modified by the mutations suggesting that the redox potential of the cytochrome c550 is not important for Photosystem II activity under normal growth conditions. A mutant lacking the cytochrome c550 was also constructed. It showed a lowered affinity for Cl– and Ca2+ as reported earlier for the cytochrome c550-less Synechocystis 6803 mutant, but it showed a shorter lived state, rather than a stabilized S2 state and rapid deactivation of the enzyme in the dark, which were characteristic of the Synechocystis mutant. It is suggested that the latter effects may be caused by loss (or weaker binding) of the other extrinsic proteins rather than a direct effect of the absence of the cytochrome c550.

Conspicuous green patches on the surface of an acidic hot mud pool located near the Rincon de la Vieja volcano (northwestern Costa Rica) consisted of apparently unialgal populations of a chloroplast-bearing euglenoid. Morphological and physiological studies showed that it is a non-flagellated photosynthetic Euglena strain able to grow in defined mineral media at temperatures up to 40°C and exhibiting higher thermotolerance than Euglena gracilis SAG 5/15 in photosynthetic activity analyses. Molecular phylogeny studies using 18S rDNA and GapC genes indicated that this strain is closely related to Euglena mutabilis, another acid-tolerant photosynthetic euglenoid, forming a clade deeply rooted in the Euglenales lineage. To our knowledge this is the most thermotolerant euglenoid described so far and the first Euglenozoan strain reported to inhabit acidic hot aquatic habitats.

The electron transfer from the heme of cytochrome c to the bacteriochlorophill dimer in reaction centers of photosynthetic purple bacteria Rps. sulfoviridis is studied by laser flash photolysis at 40–296 K in conditions where one, two, or three cytochrome hemes are chemically reduced. In the model used for the electron transfer kinetics, the protein relaxation is described with a temperature-independent oscillatory coordinate and a temperature-dependent diffusion coordinate, with the protein dielectric relaxation times widely distributed along the diffusion coordinate. It is found that all the protein complexes can be divided into proteins with fast (k et = 107 to 10–4 s–1) and slow (k et ≪ 100 s–1) electron transfer. These populations presumably differ by the protonation state of the functional group. The contribution of the oscillatory and diffusion coordinates alters, which severely affects k et. Parameters V ab, ΔG, λ, τ0, and β for these reactions are determined.

Diffuse superficial siderosis of the central nervous system (CNS) is a rare condition due to hemosiderin deposits in the subpial layers of the brain and spinal cord. The source of chronic or recurrent bleeding into the subarachnoid space is detected in only 50 % of cases. The most characteristic symptoms are cerebellar ataxia and sensorineural hearing impairment. T2-weighted gradient echo magnetic resonance imaging constitutes the diagnostic method of choice.We report four patients of diffuse superficial siderosis of the CNS associated to cerebral amyloid angiopathy, oral anticoagulation, schwannoma VIII, and without known source of bleeding in one case. Two patients developed cerebellar ataxia, three of them present transient focal neurological episodes, one dementia and, the last one, the diffuse superficial siderosis of the CNS is a radiological finding. No clinical progression was observed during follow-up (2-11 years) in three of them. The patient with cerebral amyloid angiopathy progresses to dementia.Transient focal neurological episodes were the most common symptom in our cases of diffuse superficial siderosis of the CNS. The natural history of this condition is not very known and may be regarded as a radiological finding.Siderosis superficial difusa del sistema nervioso central: descripcion de cuatro casos y revision de la bibliografia.Introduccion. La siderosis superficial difusa del sistema nervioso central (SNC) es una rara condicion debida a depositos de hemosiderina en las capas subpiales del cerebro y la medula espinal. La fuente de sangrado cronico o recurrente en el espacio subaracnoideo se detecta solo en un 50% de los casos. Los sintomas mas caracteristicos son ataxia cerebelosa e hipoacusia neurosensorial. Las secuencias eco de gradiente potenciadas en T2 de resonancia magnetica constituyen el metodo diagnostico de eleccion. Casos clinicos. Presentamos cuatro pacientes con siderosis superficial difusa del SNC relacionada con angiopatia amiloide, anticoagulacion oral, schwannoma del VIII par craneal y sin fuente de sangrado conocida en un caso. Dos pacientes desarrollaron ataxia cerebelosa; tres de ellos, episodios recurrentes de alteracion focal neurologica; uno, demencia; y el cuarto es un hallazgo radiologico. No se objetivo progresion clinica durante el seguimiento (2-11 años) en tres de ellos. El paciente con angiopatia amiloide evoluciono a demencia. Conclusiones. Los episodios recurrentes de alteracion focal neurologica son los sintomas mas frecuentes en nuestros casos de siderosis superficial difusa del SNC. La evolucion natural de esta condicion no se conoce bien y puede constituir un hallazgo radiologico.

Factors controlling the redox properties of the two conventional forms of cytochrome b559, i.e. the unstable high-potential form and the stable low-potential form, have been further investigated using PSII-enriched membranes from pea and spinach chloroplasts. The redox potential of the stable form of cytochrome b559 is pH independent both above pH 7.5 (E'm approximately +110 mV) and below pH 6.0 (E'm approximately +203 mV), but it changes with a slope of 58 mV per pH unit between these two pH values. Thus, cytochrome b559 seems to have a single ionizing group influencing its redox potential, with a higher affinity for protons in the reduced form (pK(red) = 7.5) and a lower affinity in the oxidized form (pK(ox) = 6.0); consequently, one unprotonated low-potential form (LP) and one protonated intermediate-potential form (IP). The redox potential of the high-potential form (HP) is pH-independent between pH 5.0 and 8.0, but its relative content (compared to the total amount of protein) decreases progressively above pH 7.0. This conversion to the stable LP form is interpreted as corresponding to the loss of a proton by one ionizing group, the protonation of which is essential for maintaining the unstable HP state. According to chemical modification experiments with diethylpyrocarbonate, one of the two histidine ligands of the heme seems to be the ionizing group responsible for the existence of both the protonated IP and HP forms. It is proposed that the difference between the IP and HP forms is due to the formation of an additional hydrogen bond between the protonated histidine and the protein in the HP state that stabilizes a special hydrophobic heme environment responsible for its high redox potential.

Kinetics of electron transfer from soluble cytochrome c2 to the tetraheme cytochrome c have been measured in isolated reaction centers and in membrane fragments of the photosynthetic purple bacterium Rhodopseudomonas viridis by time-resolved flash absorption spectroscopy. Absorbance changes kinetics in the region of cytochrome α-bands (540–560 nm) were measured at 21 °C under redox conditions where the two high-potential hemes (c-559 and c-556) of the tetraheme cytochrome were chemically reduced. After flash excitation, the heme c-559 donates an electron to the special pair of bacteriochlorophylls and is then re-reduced by heme c-556. The data show that oxidized heme c-556 is subsequently re-reduced by electron transfer from reduced cytochrome c2 present in the solution. The rate of this reaction has a non-linear dependence on the concentration of cytochrome c2, suggesting a (minimal) two-step mechanism involving the f ormation of a complex between cytochrome c2 and the reaction center, followed by intracomplex electron transfer. To explain the monophasic character of the reaction kinetics, we propose a collisional mechanism where the lifetime of the temporary complex is short compared to electron transfer. The limit of the halftime of the bimolecular process when extrapolated to high concentrations of cytochrome c2 is 60 ± 20 μs. There is a large ionic strength effect on the kinetics of electron transfer from cytochrome c2 to heme c-556. The pseudofirst-order rate constant decreases from 1.1 × 107 M-1 s-1 to 1.3 × 106 M-1 s-1 when the ionic strength is increased from 1 to 1000 mM. The maximum rate (1.1 × 107 M-1 s-1) was obtained at about 1 mM ionic strength. This dependence of the rate on ionic strength s uggests that attractive electrostatic interactions contribute to the binding of cytochrome c2 with the tetraheme cytochrome. On the basis of our data and of previous molecular modelling, it is proposed that cytochrome c2 docks close to the low-potential heme c-554 and reduces heme c-556 via c-554.

Isolated reaction centers of Rhodopseudomonas viridis with the two high-potential hemes reduced were illuminated at 5 K. Difference spectra show a bleaching of the heme c-556 alpha bands and a red shift of the Soret band. These effects are reversed by warming to around 80 K. They are not induced by near infra-red light absorbed by the chlorine pigments of the reaction centers and they are not associated with electron transfer from P to QA. It is concluded that, following direct excitation, heme c-556 becomes five-coordinated. We find no evidence of a significant photooxidation of heme c-559 under the same conditions.

Electron transfer from the proximal heme c -559 to the primary donor P has been studied in reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis in which the tyrosine residue L162 was replaced by threonine. In the wild type, when the two high-potential hemes of the tetraheme cytochrome are reduced before flash excitation, a rapid electron transfer ( t 1/2 =190 ns) observed at ambient temperature disappears below 190 K. In the mutant, the reaction is partly maintained down to 8 K, leading to irreversible charge separation. The reaction rate is nearly temperature-independent between 294 K and 8 K ( t 1/2 ≈450 ns). The different behavior of wild type and mutant reaction centers is attributed to differences in a network of water molecules, the freezing of which may block structural reorganizations associated with cytochrome oxidation, in the wild type but not in the mutant.

Cytochrome b559 is an essential component of the photosystem II reaction center in photosynthetic oxygen-evolving organisms, but its function still remains unclear. The use of photosystem II preparations from Thermosynechococcus elongatus of high integrity and activity allowed us to measure for the first time the influence of cytochrome b559 mutations on its midpoint redox potential and on the reduction of the cytochrome b559 by the plastoquinone pool (or QB). In this work, five mutants having a mutation in the α-subunit (I14A, I14S, R18S, I27A and I27T) and one in the β-subunit (F32Y) of cytochrome b559 have been investigated. All the mutations led to a destabilization of the high potential form of the cytochrome b559. The midpoint redox potential of the high potential form was significantly altered in the αR18S and αI27T mutant strains. The αR18S strain also showed a high sensitivity to photoinhibitory illumination and an altered oxidase activity. This was suggested by measurements of light induced oxidation and dark re-reduction of the cytochrome b559 showing that under conditions of a non-functional water oxidation system, once the cytochrome is oxidized by P680+, the yield of its reduction by QB or the PQ pool was smaller and the kinetic slower in the αR18S mutant than in the wild-type strain. Thus, the extremely positive redox potential of the high potential form of cytochrome b559 could be necessary to ensure efficient oxidation of the PQ pool and to function as an electron reservoir replacing the water oxidation system when it is not operating.

Cytochrome c550 (cyt c550), which is one of the extrinsic proteins of photosystem II (PSII), is only present in cyanobacteria and red algae. Although this cytochrome has been reported to stabilize the binding of Ca2+ and Cl− ions, which are essential for activity of PSII, the specific function of heme is not yet clear. The reported negative values of the midpoint redox potential (E m) of cyt c550 (−300 mV in the soluble state and −80 mV when associated with PSII) appear to be incompatible with a redox function in PSII. It has been reported that the E m of QA in PSII-enriched membranes was affected by the presence of redox mediators at low ambient potentials. We have carried out new measurements of E m of cyt c550 associated to PSII changing the type and number of redox mediators used. We have determined that the E m of cyt c550 is about +200 mV in the absence of mediators or in the presence of a very limited number of mediators. Our results suggest that the highly reducing conditions reached in the presence of mediators, favor the reduction of a PSII component, most likely the Mn cluster, thereby inducing alterations in protein, the heme environment and consequently the E m of the heme. The new value of E m of cyt c550 opens the possibility of a redox function for this protein.

We performed spectroscopic and functional characterization on cyanobacterium Synechocystis PCC6803 with mutations of charged residues of the cytoplasmic side of cytochrome (Cyt) b 559 in photosystem II (PSII). All of the mutant cells grew photoautotrophically and assembled stable PSII. However, R7Eα, R17Eα and R17Lβ mutant cells grew significantly slower and were more susceptible to photoinhibition than wild-type cells. The adverse effects of the arginine mutations on the activity and the stability of PSII were in the following order (R17Lβ > R7Eα > R17Eα and R17Aα). All these arginine mutants exhibited normal period-four oscillation in oxygen yield. Thermoluminescence characteristics indicated a slight decrease in the stability of the S 3 Q B − /S 2 Q B − charge pairs in the R7Eα and R17Lβ mutant cells. R7Eα and R17Lβ PSII core complexes contained predominantly the low potential form of Cyt b 559 . EPR results indicated the displacement of one of the two axial ligands to the heme of Cyt b 559 in R7Eα and R17Lβ mutant reaction centers. Our results demonstrate that the electrostatic interactions between these arginine residues and the heme propionates of Cyt b 559 are important to the structure and redox properties of Cyt b 559 . In addition, the blue light-induced nonphotochemical quenching was significantly attenuated and its recovery was accelerated in the R7Lα and R17Lβ mutant cells. Furthermore, ultra performance liquid chromatography–mass spectrometry results showed that the PQ pool was more reduced in the R7Eα and R17Lβ mutant cells than wild-type cells in the dark. Our data support a functional role of Cyt b 559 in protection of PSII under photoinhibition conditions in vivo.

El pdf del artículo es la versión pre-print., A study of the in vitro reconstitution of sugar beet cytochrome b 559 of the photosystem II is described. Both α and β cytochrome subunits were first cloned and expressed in Escherichia coli. In vitro reconstitution of this cytochrome was carried out with partially purified recombinant subunits from inclusion bodies. Reconstitution with commercial heme of both (αα) and (ββ) homodimers and (αβ) heterodimer was possible, the latter being more efficient. The absorption spectra of these reconstituted samples were similar to that of the native heterodimer cytochrome b 559 form. As shown by electron paramagnetic resonance and potentiometry, most of the reconstituted cytochrome corresponded to a low spin form with a midpoint redox potential +36 mV, similar to that from the native purified cytochrome b 559. Furthermore, during the expression of sugar beet and Synechocystis sp. PCC 6803 cytochrome b 559 subunits, part of the protein subunits were incorporated into the host bacterial inner membrane, but only in the case of the β subunit from the cyanobacterium the formation of a cytochrome b 559-like structure with the bacterial endogenous heme was observed. The reason for that surprising result is unknown. This in vivo formed (ββ) homodimer cytochrome b 559-like structure showed similar absorption and electron paramagnetic resonance spectral properties as the native purified cytochrome b 559. A higher midpoint redox potential (+126 mV) was detected in the in vivo formed protein compared to the in vitro reconstituted form, most likely due to a more hydrophobic environment imposed by the lipid membrane surrounding the heme., This work was supported by Grants AGL2008-00377, MAT2008-03461, and BFU2007-68107-C02-01 from the Spanish Ministry of Science and Innovation (MICINN), PADI CVI-261 from the Andalusia Regional Government, and DGA-GC E33 and DGA-GE B18 from Aragon Regional Government. All these Grants were partially financed by the EU FEDER Program. M. A. Luján would like to thank the FPI Fellowship Program of the MICINN for financial support.

The aim of this paper is to analyze how the dispersed generators can be used to effectively control the voltage of the distribution network. The technical and economical viability of this proposal can be assessed throughout a systematic analysis of how the voltage of the point of common coupling (PCC) increases as a function of the injected active power, and the required reactive power needed to maintain the voltage of the PCC to a given value. (4 pages)

Cytochrome c550 (cyt c550) is a membrane component of the PSII complex in cyanobacteria and some eukaryotic algae, such as red and brown algae. Cyt c550 presents a bis-histidine heme coordination which is very unusual for monoheme c-type cytochromes. In PSII, the cyt c550 with the other extrinsic proteins stabilizes the binding of Cl¿ and Ca2+ ions to the oxygen evolving complex and protects the Mn4Ca cluster from attack by bulk reductants. The role (if there is one) of the heme of the cyt c550 is unknown. The low midpoint redox potential (Em) of the purified soluble form (from ¿250 to ¿314 mV) is incompatible with a redox function in PSII. However, more positive values for the Em have been obtained for the cyt c550 bound to the PSII. A very recent work has shown an Em value of +200 mV. These data open the possibility of a redox function for this protein in electron transfer in PSII. Despite the long distance (22 Å) between cyt c550 and the nearest redox cofactor (Mn4Ca cluster), an electron transfer reaction between these components is possible. Some kind of protective cycle involving a soluble redox component in the lumen has also been proposed. The aim of this article is to review previous studies done on cyt c550 and to consider its function in the light of the new results obtained in recent years. The emphasis is on the physical properties of the heme and its redox properties. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Summary Cytochrome b 559 (Cyt b 559) is an intrinsic and essential component of the photosystem II (PSII) reaction center, but its physiological function remains yet undefined. In this study, a partial redox characterization of Cyt b 559 in photosynthetic membranes from the transformable unicellular cyanobacterium Synecborystis sp. PCC 6803 (hereafter called Synecborystis 6803) has been performed. In thylakoid membranes extracted by a very mild cell-breaking procedure, as developed in this work, only one redox form of Cyt b 559 was found, with a redox potential proper to a low-potential (LP) form. The midpoint redox potential value of this LP form has been shown to be + 170 mV at pH 7.5 in PSII-enriched membranes. In spite of a great variety of cell-breaking treatments used to prepare thylakoid membranes, it has not been possible to detect any high-potential (HP) form of Cyt b 559. The absence of this HP form is discussed in terms of its higher lability in Synecborystis 6803 as compared with other cyanobacteria and higher plants. Alternatively, the possibility is considered that a HP form of Cyt b 559 does not occur in Synecborystis 6803 because it can not be properly stabilized in the membrane environment.

This research was originally published in Journal of Biological Chemistry. Fernando Guerrero, Arezki Sedoud, Diana Kirilovsky, A. William Rutherford, José M. Ortega, and Mercedes Roncel. A High Redox Potential Form of Cytochrome c550 in Photosystem II from Thermosynechococcus elongatus. Journal of Biological Chemistry. 2011. Vol 286: 5985-5994. © the American Society for Biochemistry and Molecular Biology, Cytochrome c550 (cyt c550) is a component of photosystem II (PSII) from cyanobacteria, red algae, and some other eukaryotic algae. Its physiological role remains unclear. In the present work, measurements of the midpoint redox potential (Em) were performed using intact PSII core complexes preparations from a histidine-tagged PSII mutant strain of the thermophilic cyanobacterium Thermosynechococcus (T.) elongatus. When redox titrations were done in the absence of redox mediators, an Em value of +200 mV was obtained for cyt c550. This value is ∼300 mV more positive than that previously measured in the presence of mediators (Em = −80 mV). The shift from the high potential form (Em = +200 mV) to the low potential form (Em = −80 mV) of cyt c550 is attributed to conformational changes, triggered by the reduction of a component of PSII that is sequestered and out of equilibrium with the medium, most likely the Mn4Ca cluster. This reduction can occur when reduced low potential redox mediators are present or under highly reducing conditions even in the absence of mediators. Based on these observations, it is suggested that the Em of +200 mV obtained without mediators could be the physiological redox potential of the cyt c550 in PSII. This value opens the possibility of a redox function for cyt c550 in PSII., This work was supported by grants from the Ministry of Education and Culture of Spain (BFU2007- 68107-C02-01/BMC) and Andalusia Government (PAI CVI-261). The work done in France was supported by the EU/Energy Network project SOLAR-H2 (FP7 contract 212508).

The microalgae Chlamydomonas reinhardtii and Chlorella sp. CCAP 211/84 were grown autotrophically and mixotrophically and their thermoluminescence emissions were recorded above 0 °C after excitation by 1, 2 or 3 xenon flashes or by continuous far-red light. An oscillation of the B band intensity according to the number of flashes was always observed, with a maximum after 2 flashes, accompanied by a downshift of the B band temperature maximum in mixotrophic compared to autotrophic grown cells, indicative of a dark stable pH gradient. Moreover, new flash-induced bands emerged in mixotrophic Chlamydomonas grown cells, at temperatures higher than that of the B band. In contrast to the afterglow band observed in higher plants, in Chlamydomonas these bands were not inducible by far-red light, were fully suppressed by 2 μM antimycin A, and peaked at different temperatures depending on the flash number and growth stage, with higher temperature maxima in cells at a stationary compared to an exponential growth stage. These differences are discussed according to the particular properties of cyclic electron transfer pathways in C. reinhardtii. © 2011 Elsevier B.V. All rights reserved.

A soluble monoheme c-type cytochrome (cytochrome c6) has been isolated from the green alga Monoraphidium braunii. It has a molecular mass of 9.3 kDa, an isoelectric point of 3.6 and a reduction potential of 358 mV at pH 7. The determined amino acid sequence allows its classification as a class-I c-type cytochrome. The ferric and ferrous cytochrome forms and their pH equilibria have been studied using 1H-NMR, ultraviolet/visible, EPR and Mossbauer spectroscopies. The pH equilibria are complex, several pKa values and pH-dependent forms being observed. The amino acid sequence, the reduction-potential value and the visible and NMR spectroscopies data in the pH range 4-9 indicate that the heme iron has a methionine-histidine axial coordination. However, the EPR and Mossbauer data obtained for the ferricytochrome show that in this pH range two distinct forms are present: form I, gz = 3.27, gy = 2.05 and gx = 1.05; form II, gz = 2.95, gy = 2.29 and gx = 1.43. While form I has crystal-field parameters typical of a methionine-histidine coordination, those associated with form II would suggest a histidine-histidine axial ligation. This possibility was extensively analyzed by spectroscopic methods and by chemical modification of a histidine residue. It was concluded that form II actually corresponds to an unusual type of methionine-histidine axial coordination. Straightforward examples of this type of coordination have recently been found in other c-type hemeproteins [Teixeira, M., Campos, A. P., Aguiar, A. P., Costa, H. S., Santos, H., Turner, D. L. & Xavier, A. V. (1993) FEBS Lett. 317, 233-236], corroborating our proposal. Since both forms, with very distinct crystal-field parameters, are shown to have the same reduction potential, it may be concluded that the axial and rhombic distortions of the heme-iron ligand field cannot be directly correlated with the heme-reduction potential. The pH-dependence studies have also shown that the form I and form II are interconvertible, with pKa approximately 5. To establish a possible physiological significance for this process, in particular for the interaction of the cytochrome with the membrane-bound electron-transfer complexes b6f and photosystem I, the effect of surfactants on the spectroscopic characteristics of cytochrome c6 has been studied.

Kinetics of electron transfer from the bound tetraheme cytochrome c to the primary donor (P) have been measured in isolated reaction centers of the purple bacterium Rhodopseudomonas viridis by time-resolved flash absorption spectroscopy. The influence of two major parameters has been studied: temperature (7-305 K) and the redox state of the cytochrome. Most experiments were done with one heme (c-559), two hemes (c-559 and c-556), or three hemes (c-559, c-556, and c-552) poised in a reduced state before the flash. Measurements were done at 1283 nm in the absorption band of P+, and in the region of cytochrome alpha-bands. At room temperature, c-559 donates an electron to P+ with a half-time of 115, 190, or 230 ns (with three, two, or one heme reduced, respectively) and is then eventually rereduced by c-556 (t1/2 = 1.7 microseconds) or by c-552 (in less than 40 ns). The kinetics also include a minor microsecond phase of P+ reduction. At decreasing temperatures, the polyphasic character of P+ rereduction is accentuated. Fast phases (115 ns-10 microseconds) are slightly slowed down, following Arrhenius behavior with a weak activation energy (3.6-8.6 kJ.mol-1), until they become temperature-independent. Their extent decreases rather sharply, at temperatures which vary according to the redox poising: 250, 210, or 80 K when one, two, or three hemes are reduced, respectively. In the last case, P+ can still be reduced at low temperature, apparently directly by c-552 (t1/2 = 1.1 ms, nearly temperature-independent).(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome b559 is an intrinsic and essential component of the photosystem II reaction centre in all photosynthetic oxygen- evolving organisms, but its function, although widely investigated, still remains unresolved. Most of the functional hypotheses propose that cytochrome b559 may participate in secondary electron transfer pathways protecting photosystem II against oxidative damage. Mutational studies have not succeeded in demonstrating this redox function because most of the cytochrome b559 mutants obtained are impaired in the functional assembly of photosystem II holocomplex. We have constructed a series of sitedirected mutants of cytochrome b559, each carrying a single amino acid substitution, in the thermophilic cyanobacterium Thermosynechococcus elongatus, in order to modify the redox potential of the heme without altering the assembly properties of photosystem II. We have obtained 19 mutant strains of cytochrome b559. All the mutants grew photoautotrophically at a rate similar to that of the wild-type. Some of these mutants showed relevant differences in redox properties of cytochrome b559 compared to wild-type. The α-R18S mutant strain showed the most important effects on redox potential and photosystem II activity.

Photosynthesis consists essentially in the conversion, by the plant kingdom, of sunlight energy into chemical energy (cell material and molecular oxygen). From a physicochemical point of view, photosynthesis is intrinsically a light-driven oxidation—reduction/acid—base process. In the course of photosynthesis, water is oxidized to molecular oxygen, whereas carbon dioxide, nitrate or dinitrogen, and sulfate are respectively reduced to carbohydrate, ammonia and sulfide; water is moreover ionized, in similar amounts, into protons and hydroxide anions. Phosphorus does not change its oxidation state, but orthophosphate becomes energized to metaphosphate, at the expense of the ionization products of water, in a peculiar acid—base process. Metaphosphate is mostly used as an energy shuttle in many cell processes, among them in the reduction and assimilation of the primordial bioelements, as well as in the polymerization of the resulting monomers — sugars, lipid components, amino acids, nucleotides — and deenergizes itself back to orthophosphate, again in acid—base reactions. The role of the oxide anion, that is, an oxygen atom with two additional electrons, O 2− , in these bioenergetic processes is especially discussed.

The definitive version is available at: http://www.sciencedirect.com/science//journal/00052728, Anomalies in photosynthetic activity of the soybean cell line STR7, carrying a single mutation (S268P) in the chloroplastic gene psbA that codes for the D1 protein of the photosystem II, have been examined using different spectroscopic techniques. Thermoluminescence emission experiments have shown important differences between STR7 mutant and wild type cells. The afterglow band induced by both white light flashes and far-red continuous illumination was downshifted by about 4 °C and the Q band was upshifted by 5 °C. High temperature thermoluminescence measurements suggested a higher level of lipid peroxidation in mutant thylakoid membranes. In addition, the reduction rate of P700+ was significantly accelerated in STR7 suggesting that the mutation led to an activation of the photosystem I cyclic electron flow. Modulated fluorescence measurements performed at room temperature as well as fluorescence emission spectra at 77 K revealed that the STR7 mutant is defective in state transitions. Here, we discuss the hypothesis that activation of the cyclic electron flow in STR7 cells may be a mechanism to compensate the reduced activity of photosystem II caused by the mutation. We also propose that the impaired state transitions in the STR7 cells may be due to alterations in thylakoid membrane properties induced by a low content of unsaturated lipids., This work was supported by grants from the Ministry of Education and Culture of Spain (BFU-BMC2004-04914-C02-01, BMC2002-00031 and BFU-BMC2005-07422-C02-01) and Andalusia Government (PAI CVI-261).