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Doxorubicin is an anthracycline-based chemotherapeutic that causes myotoxicity with symptoms persisting beyond treatment. Patients experience muscle pain, weakness, fatigue, and atrophy, but the underlying mechanisms are poorly understood. Studies investigating doxorubicin-induced myotoxicity have reported disrupted mitochondrial function. Mitochondria are responsible for regulating both cellular energy status and Ca(2+) handling, both of which impact contractile function. Moreover, loss of mitochondrial integrity may initiate muscle atrophy. Skeletal muscle mitochondrial dysregulation may therefore contribute to an overall loss of skeletal muscle quality and performance that may be mitigated by appropriately targeted mitochondrial therapies. We therefore assessed the impact of doxorubicin on muscle performance and applied a multiplexed assay platform to diagnose alterations in mitochondrial respiratory control. Mice received a clinically relevant dose of doxorubicin delivered systemically and were euthanized 72 h later. We measured extensor digitorum longus and soleus muscle forces, fatigue, and contractile kinetics in vitro, along with Ca(2+) uptake in isolated sarcoplasmic reticulum. Isolated skeletal muscle mitochondria were used for real-time respirometry or frozen for protein content and activity assays. Doxorubicin impaired muscle performance, which was indicated by reduced force production, fatigue resistance, and sarcoplasmic reticulum–Ca(2+) uptake, which were associated with a substrate-independent reduction in respiration and membrane potential but no changes in the NAD(P)H/NAD(P)(+) redox state. Protein content and dehydrogenase activity results corroborated these findings, indicating that doxorubicin-induced mitochondrial impairments are located upstream of ATP synthase within the electron transport system. Collectively, doxorubicin-induced lesions likely span mitochondrial complexes I–IV, providing potential targets for alleviating doxorubicin myotoxicity.

Polyethylenimines (PEIs) are highly efficient non-viral transfectants, but can induce cell death through poorly understood necrotic and apoptotic processes as well as autophagy. Through high resolution respirometry studies in H1299 cells we demonstrate that the 25kDa branched polyethylenimine (25k-PEI-B), in a concentration and time-dependent manner, facilitates mitochondrial proton leak and inhibits the electron transport system. These events were associated with gradual reduction of the mitochondrial membrane potential and mitochondrial ATP synthesis. The intracellular ATP levels further declined as a consequence of PEI-mediated plasma membrane damage and subsequent ATP leakage to the extracellular medium. Studies with freshly isolated mouse liver mitochondria corroborated with bioenergetic findings and demonstrated parallel polycation concentration- and time-dependent changes in state 2 and state 4o oxygen flux as well as lowered ADP phosphorylation (state 3) and mitochondrial ATP synthesis. Polycation-mediated reduction of electron transport system activity was further demonstrated in ‘broken mitochondria’ (freeze-thawed mitochondrial preparations). Moreover, by using both high-resolution respirometry and spectrophotometry analysis of cytochrome c oxidase activity we were able to identify complex IV (cytochrome c oxidase) as a likely specific site of PEI mediated inhibition within the electron transport system. Unraveling the mechanisms of PEI-mediated mitochondrial energy crisis is central for combinatorial design of safer polymeric non-viral gene delivery systems.

Nanopesticides are widely applied in modern agricultural systems to replace traditional pesticides, which inevitably leads to their accumulation in soils. Nanopesticides based on copper oxide nanoparticles (CuO NPs) may affect the soil nitrogen cycle, such as the denitrification process; however, the mechanism remains unclear. Here, acute exposure experiments for 60 h were conducted to explore the effects of CuO NPs (10, 100, 500 mg kg−1) on denitrification. In this study, Cu speciation, activities of denitrifying enzymes, electron transport system activity (ETSA), expression of denitrifying functional genes, composition of bacterial communities and reactive oxygen species (ROS) were determined. In all treatments, Cu ions was the dominant form and responsible for the toxicity of CuO NPs. The results indicated that CuO NPs treatments at 500 mg kg−1 remarkably inhibited denitrification, led to an 11-fold increase in NO3− accumulation and N2O emission rates decrease by 10.2–24.1%. In the denitrification process, the activities of nitrate reductase and nitric oxide reductase reduced by 21.1–42.1% and 10.3–16.3%, respectively, which may be a reason for the negative effect of CuO NPs. In addition, ETSA was significantly inhibited with CuO NPs applications, which reflects the ability of denitrification to accept electrons. Denitrifying functional genes and bacterial communities composition were changed, thus further influencing the denitrification process. ROS analysis showed that there were no significant differences among NPs treatments. This research improves the understanding of CuO NPs impact on soil denitrification. Further attention should be paid to the nitrogen transformation in agricultural soils in the presence of nanopesticides.

Fish expend significant amounts of energy to handle the numerous potentially stressful biotic and abiotic factors that they commonly encounter in aquatic environments. This universal requirement for energy singularizes mitochondria, the primary cellular energy transformers, as fundamental drivers of responses to environmental change. Our study probed the interacting effects of thermal stress, hypoxia-reoxygenation (HRO) and copper (Cu) exposure in rainbow trout to test the prediction that they act jointly to impair mitochondrial function. Rainbow trout were acclimated to 11 (controls) or 20°C for 2 months. Liver mitochondria were then isolated and their responses in vitro to Cu (0-20μM) without and with HRO were assessed. Sequential inhibition and activation of mitochondrial electron transport system (ETS) enzyme complexes permitted the measurement of respiratory activities supported by complex I-IV (CI-IV) in one run. The results showed that warm acclimation reduced fish and liver weights but increased mitochondrial protein indicating impairment of energy metabolism, increased synthesis of defense proteins and/or reduced liver water content. Whereas acute rise (11→20°C) in temperature increased mitochondrial oxidation rates supported by CI-IV, warm acclimation reduced the maximal (state 3) and increased the basal (state 4) respiration leading to global uncoupling of oxidative phosphorylation (OXPHOS). HRO profoundly inhibited both maximal and basal respiration rates supported by CI-IV, reduced RCR for all except CII and lowered CI:CII respiration ratio, an indication of decreased OXPHOS efficiency. The effects of Cu were less pronounced but more variable and included inhibition of CII-IV maximal respiration rates and stimulation of both CI and CIII basal respiration rates. Surprisingly, only CII and CIII indices exhibited significant 3-way interactions whereas 2-way interactions of acclimation either with Cu or HRO were portrayed mostly by CIV, and those of HRO and Cu were most common in CI and II respiratory indices. Our study suggests that warm acclimation blunts sensitivity of the ETS to temperature rise and that HRO and warm acclimation impose mitochondrial changes that sensitize the ETS to Cu. Overall, our study highlights the significance of the ETS in mitochondrial bioenergetic dysfunction caused by thermal stress, HRO and Cu exposure.

Measuring electron transport system (ETS) activity in zooplankton provides an index of respiration, theoretically, the potential respiration rate. We apply the ETS technique to estimate potential respiration and carbon demand from the zooplankton community in the upper 200 m of the water column near the Balearic Islands. The investigation was focused on two areas with different oceanographic conditions: the Balearic and Algerian subbasins. It compared the biomass, potential respiration and specific potential respiration of different size fractions (53–200, 200–500, > 500 μm) in both areas. In these regions the largest contribution to respiration was found in the larger sizes. The specific respiration (per unit biomass) was greater in smaller fractions, indicating that they have a more active metabolism. Both biomass and potential respiration increased in the Algerian subbasin and for both regions biomass and potential respiration were greater in shallow waters over the continental shelf (

The mitochondrion is the organelle responsible for generation of most usable energy in a cell. It also plays an important role in a series of physiological processes such as apoptosis and proliferation. Although previous studies have demonstrated that nicotine modulates the morphology and function of mitochondria, the mechanism(s) underlying these effects is largely unknown. In this study, using a microarray consisting of 4,793 clones derived from a mouse dopamine cDNA library, we profiled the gene expression patterns for six brain regions (amygdala, hippocampus, nucleus accumbens, prefrontal cortex, striatum, and ventral tegmental area) of female Sprague-Dawley rats subjected to nicotine treatment for 7 days through osmotic minipump infusion. We identified a number of genes and pathways, including components of the electron transport system of mitochondria, such as cytochrome c oxidase subunit I (Mt-co1), Mt-co2, Mt-co3, cytochrome b (Mt-cyb), mitochondrial NADH dehydrogenase 4 (Mt-nd4), and Mt-nd6, that were significantly modulated by nicotine in multiple brain regions. Bioinformatics analysis provided evidence that Gene Ontology categories related to the electron transport system were overrepresented in each brain region. Finally, the results from the microarray analysis were verified by quantitative RT-PCR for four representative genes. Together, our findings imply that mitochondria are involved in neuronal adaptation to chronic nicotine exposure.

In order to better understand how surfactants affect biodegradation of hydrophobic organic compounds (HOCs), Tween 80 and sodium dodecyl benzene sulfonate (SDBS), were selected to investigate effects on cell surface hydrophobicity (CSH), electron transport system (ETS) activities and phenanthrene biodegradation by Citrobacter sp. SA01. Tween 80 and SDBS increased CSH by 19.8–25.2%, ETS activities by 352.1–376.0 μmol/g min, catechol 1,2-dioxygenase (C12) activities by 50.8–52.7 U/L, and phenanthrene biodegradation by 8.9–17.2% separately in the presence of 50 mg/L of surfactants as compared to in their absence. Lipopolysaccharide (LPS) release was 334.7 μg/mg in the presence of both surfactants whereas in their absence only 8.6–44.4 μg/mg of LPS was released. Thus, enhanced LPS release probably increased ETS and C12 activities as well as phenanthrene biodegradation by increasing CSH. The results demonstrate that surfactant-enhanced CSH provides a simple, yet effective strategy for field applications of surfactant-enhanced bioremediation of HOCs.

Nitric oxide ({radical dot}NO) generated by the dissociation of S-nitrosoglutathione or added as gaseous solution, inhibits the oxidation of exogenous NADH supported by the activity of the cytosolic NADH/cyto-c electron transport pathway. The inhibition is immediate, very strong, higher at lower oxygen concentration, independent on the {radical dot}NO concentration and remains constant as long as {radical dot}NO is no more available and then is spontaneously removed. The data obtained, not in contrast with those reported with isolated cytochrome oxidase (Cox), strengthen a new concept: reduced cytochrome c (cyto-c) and {radical dot}NO behave as two substrates of Cox, which promotes their oxidation with molecular oxygen as a co-substrate. In the presence of {radical dot}NO, Cox exhibits the property of switching from cyto-c oxidase to {radical dot}NO oxidase activity. With an "all or nothing" process Cox becomes an efficient {radical dot}NO scavenger. The persistence of membrane potential, even in the presence of high inhibition of oxygen uptake, could be tentatively correlated to the protective effect of {radical dot}NO on the ischaemic-reperfusion injury

An investigation has been made of the points of coupling of four nonpermeable electron acceptors e.g., alpha-lipoic acid (ALA), 5,5'-dithiobis (2-nitroaniline-N-sulphonic acid) (DTNS), 1,2-naphthoquinone-4-sulphonic acid (NQSA) and ferricyanide which are mainly reduced via an interaction with the redox sites present in the plasma membrane of Leishmania donovani promastigotes. ALA, DTNS, NQSA and ferricyanide reduction and part of O2 reduction is shown to take place on the exoplasmic face of the cell, for it is affected by external pH and agents that react with the external surface. Redox enzymes of the transplasma membrane electron transport system orderly transfer electron from one redox carrier to the next with the molecular oxygen as the final electron acceptor. The redox carriers mediate the transfer of electrons from metabolically generated reductant to nonpermeable electron acceptors and oxygen. At a pH of 6.4, respiration of Leishmania cells on glucose substrate shut down almost completely upon addition of an uncoupler FCCP and K+-ionophore valinomycin. The most pronounced effects on O2 uptake were obtained by treatment with antimycin A, 2-heptadecyl-4-hydroxyquinone-N-oxide, paracholoromercuribenzene sulphonic acid and trifluoperazine. Relatively smaller effects were obtained by treatment with potassium cyanide. Inhibition observed with respect to the reduction of the electron acceptors ALA, DTNS, NQSA and ferricyanide was not similar in most cases. The redox chain appears to be branched at several points and it is suggested that this redox chain incorporate iron-sulphur center, b-cytochromes, cyanide insensitive oxygen redox site, Na+ and K+ channel, capsaicin inhibited energy coupling site and trifluoperazine inhibited energy linked P-type ATPase. We analyzed the influence of ionic composition of the medium on reduction of electron acceptors in Leishmania donovani promastigotes. Our data suggest that K+ have some role for ALA reduction and Na+ for ferricyanide reduction. No significant effects were found with DTNS and NQSA reduction when Na+ or K+ was omitted from the medium. Stimulation of ALA, DTNS, NQSA and ferricyanide reduction was obtained by omitting Cl- from the medium. We propose that this redox system may be an energy source for control of membrane function in Leishmania cells.

In addition to ultraviolet radiation, human skin is also exposed to infrared radiation (IR) from natural sunlight. IR typically increases the skin temperature. This study examined whether or not heat shock-induced ROS stimulates MMPs in keratinocyte HaCaT cells. In HaCaT cells, heat shock was found to increase the intracellular ROS levels, including hydrogen peroxide and superoxide. The heat shock treatment induced MMP-1 and MMP-9, but not MMP-2, at the mRNA and protein levels. Moreover, heat shock caused the rapid activation of the three distinct MAPKs, ERK, JNK, and p38 kinase. The heat shock-induced expression of MMP-1 and MMP-9 was significantly suppressed by a pretreatment with the antioxidant NAC or catalase. On the other hand, SOD inhibited heat shock-induced activity of MMP-9 induction, but not MMP-1. A pretreatment with NAC or catalase, but not SOD, attenuated the phosphorylation of ERK, JNK, and p38 kinase by heat shock. The potential sites of ROS generation by heat shock along with its role in the heat shock-induced expression of MMP-1 and MMP-9 were next analyzed. These results indicate that heat shock-induced ROS is promoted via NADPH oxidase, xanthine oxidase, and mitochondria. Indeed, the NADPH oxidase and xanthine oxidase activities were increased by heat shock. Overall, the ROS produced by heat shock may play an important role in the heat shock-induced activation of MAPKs, which can induce MMP-1 and-9 expressions.

Disulfide bond formation is catalyzed in vivo by DsbA and DsbB. Here we reconstitute this oxidative folding system using purified components. We have found the sources of oxidative power for protein folding and show how disulfide bond formation is linked to cellular metabolism. We find that disulfide bond formation and the electron transport chain are directly coupled. DsbB uses quinones as electron acceptors, allowing various choices for electron transport to support disulfide bond formation. Electrons flow via cytochrome bo oxidase to oxygen under aerobic conditions or via cytochrome bd oxidase under partially anaerobic conditions. Under truly anaerobic conditions, menaquinone shuttles electrons to alternate final electron acceptors such as fumarate. This flexibility reflects the vital nature of the disulfide catalytic system.

Membranes isolated from light- and dark-grown cells of the recently established new taxon of the purple nonsulfur bacteria, Rhodoferax fermentans , gen. nov., sp. nov., have been examined. The results have been interpreted to show that the oxidative electron transport chain is branched at the ubiquinone level and does not involve rhodoquinone. Dark-grown membranes contain four b -type and three c -type membrane-bound cytochromes with E m7.0 of +371, +315, +76 and −18 mV and +298, +201 and +44 mV, respectively. No significant amount of soluble c was found in aerobic cells. Conversely, photosynthetically grown cells contain a soluble c -type haem ( α max at 551 nm, E m7.0 = +287 mV), four membrane-bound c -type haems with E m7.0 of +358, +296, +78 and −1 mV and three cytochromes b with E m7.0 of +320, +30 and −50 mV. Notably, the absence of cyt b -371 from light-grown membranes parallels the very low rate of cyt c oxidase activity catalyzed by this type of membrane. Oxido-reduction kinetics demonstrated that most of the c -type haems detected in light-grown membranes are not involved in respiration. These data suggest that the facultative phototroph Rf. fermentans is endowed with an electron transport system different rrom that of typical facultative phototrophs, e.g., Rhodobacter and Rhodospirillum species, but similar to that of green- and purple-nonsulfur genera such as Chloroflexus, Rhodocyclus and Rhodopseudomonas .

Measurements of the activity of the respiratory electron transport system (ETS) at 15 stations in the Arabian Sea during the northeast monsoon (December 1988) yield high respiration rates that do not correlate with the trends in primary productivity. The rates are unlikely to be sustained by the supply of carbon associated with the sinking particles alone, and seem to suggest a major role for dissolved and/or suspended organic matter in fuelling oxygen consumption and denitrification. The data are utilized to compute a denitrification rate of 24–33 Tg N y−1 in the Arabian Sea. This estimate agrees with the estimate based on the exports of nitrate deficits outside the denitrification zone. The ventilation time of the denitrifying layer is calculated as ∼1 year.

The factors affecting the measurement of electron transport system (ETS) activity in river biofilm through the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to iodonitrotetrazolium formazan (INT-formazan) have been studied. Methanol extracts INT-formazan more effectively than either propanol or ethanol. A concentration of 0.02% INT was chosen and samples should be incubated for less than 8 h. ETS activity is optimal at a circumneutral pH. ETS stimulators (NADH, NADPH and succinate) added as a check of the assay produced an increase in INT-formazan indicating that ETS activity was being measured. This assay is quick, easy to use and ideal for field studies.

Fluorescence, absorbance and photoacoustic methods were used to examine in situ various functional aspects of the photochemical apparatus of chloroplasts in potato leaves (Solanum tuberosum L.) briefly pre-exposed in the dark to a wide range of elevated temperatures (32°C–45°C). Measurements of the Emerson enhancement of photosynthetic O2 evolution and the flash-induced reduction of the oxidized reaction center pigment of photosystem I demonstrated that selective denaturation of photosystem II in potato leaves started at a ‘low’ temperature of 32°C. Analysis of the characteristics of chlorophyll fluorescence induction in sub- and super-saturating light revealed two targets of mild heat stress: (i) an irreversible inhibition of electron donation to PSII and (ii) a reversible reduction of excitation energy trapping by the PSII reaction centers, with the former effect being identified as the major determinant of the loss of photosynthesis. A second phase of thermal denuration of photosystem II occurred at temperatures higher than around 38°C, resulting in a dramatic loss of PSII-mediated electron transport. Measurements of chlorophyll fluorescence decay kinetics after short and long flashes of intense light indicated that high temperatures up to 42°C had no inhibitory effect on the acceptor side of photosystem II: the rate of electron transfer from the primary (QA) to the secondary (QB) electron acceptor of photosystem II and the fraction of QB-non-reducing photosystem-II centers remained unchanged whereas the intersystem electron flow appeared to be stimulated. It was also observed that photosystem-I photochemistry, as probed by the photochemical energy storage in far-red light, the quantum yield of photosystem I for the Emerson effect and the kinetics of P700 photooxidation by strong far-red light, was fully preserved in heat-treated potato leaves (at least, up to 45°C). From the presented data, one can propose the following sequence of events leading to the loss of photosynthetic electron transport in heated potato leaves: inhibition of water splitting (at leaf temperatures higher than 32°C) Q A ( > 42° C ) PSI ( > 45° C ) .

Summary Cadmium toxicity to Nostoc linckia has been investigated by studying its effect on nitrogen, phosphorus metabolism and photosynthetic processes. Cells exposed to 0.01, 0.03 and 0.05 μg mL -1 Cd, showed a concentration dependent inhibition of growth, nutrient uptake and activities of enzymes responsible for assimilation of nutrients. The Michaelis-Menten and Lineweaver-Burk plots demonstrated a non-competitive inhibition for NO 3 - but competitive for PO 4 3- and negative cooperativity for NH 4 + uptake by Cd. Nitrogenase activity was, however, delayed by 48 h under Cd stress. Alkaline phosphatase activity showed a differential behaviour of repression and derepression with respect to presence or absence of PO 4 3- in the medium under Cd stress. 14 C uptake was more susceptible to Cd than photosynthetic O 2 evolution. This study suggests that inhibition of carbon fixation was due to a Cd-induced decrease in ATP content. PS II was found to be the primary site of action of Cd for photosynthetic electron transport and was mainly responsible for Cd toxicity in Nostoc linckia .

Summary Results are presented to document the effects of different concentrations of zinc (ZnCl2) and mercury (HgCl2) on different processes of Chlorella vulgaris. The effective concentrations of Hg and Zn reducing 50 per cent (LC50) of the population of the test organism were found to be 0.5 and 2.0 µg mL-1, respectively. These concentrations of Hg and Zn reduced growth, CO2 fixation, O2 evolution, ATP content and NR activity by 56, 64, 75, 89 and 91 % and 50, 36, 57, 79 and 90 %, respectively. The test metals were also found to be highly toxic for nutrient (NO3- and NH4+) uptake. PS II was found to be the primary site of action for the two metals. A possible mechanism of Hg and Zn toxicity is discussed.

Intact cells of Rhodobacter capsulatus in the presence of myxothiazol were exposed to trains of short flashes of saturating light and the pattern of the absorbance changes due to P870, cytochrome ( c 1 + c 2 ) and the carotenoids that report on the membrane potential were monitored. Myxothiazol inhibits cyclic electron transport and therefore the extent to which electron donors and acceptors of the reaction centre are available for photochemistry is revealed. In darkened anaerobic suspensions of cells in the presence of myxothiazol, only the first two flashes in the train led to charge separation in the photosynthetic reaction centres. The results indicated that the quinone pool and quinone bound at the Q B site in the reaction centre were extensively reduced and quinone bound at Q A was partly reduced before initiation of flash excitation. Thus under these conditions, and in the absence of myxothiazol, cyclic electron transport would be restricted. In the presence of oxygen or the auxiliary oxidants trimethylamine N -oxide, NO − 3 or N 2 O, the oxidation/reduction reactions and the electrochromic absorbance changes suggested that the pool and reaction centre quinones became more oxidised. Thus, the system was poised at a potential more conducive to optimal rates of photosynthetic electron transport. By reference to experiments on the growth of Rb. capsulatus (Richardson, D.J., King, G.F., Kelly, D.J., McEwan, A.G., Ferguson, S.J. and Jackson, J.B. (1988) Arch. Microbiol. 150, 131–137), it is argued that redox poising by the auxiliary oxidants is physiologically important, especially at low light intensities. Flash train experiments reveal that over-reduction of the quinones is more severe with succinate as a carbon source than with malate and this accounts for the observation that the rate of growth on succinate is decreased more strongly at low light intensities.