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Since the 1980s, influential participants in the niche over-the-counter (OTC) derivatives markets have sought to encourage contractual standardization in the industry to mitigate the potential for unforeseen legal interruptions and ensure the enforceability of OTC derivatives contracts. The International Swaps and Derivatives Association (ISDA), a trade association and standard-setter, has spearheaded this effort; resulting in the creation and sustenance of a highly successful transnational private regulatory regime (TPRER). Most notably, ISDA has generated a standardized boilerplate contract for OTC derivatives, known as the ‘ISDA Master Agreement’. However, the TPRER within which the ISDA Master Agreement operates displays some intriguing features and paradoxes. Chief amongst these paradoxes is that, while this TPRER appears at first glance to be highly legalistic and formal, indications are that rates of formal litigation between members of the regulatory regime have traditionally been low relative to the size of the market (the total notional amount of OTC derivatives contracts outstanding at the end of 2011 was estimated at US$648 trillion).

It has frequently been claimed that over-the-counter (OTC) derivatives were, by and large, not directly regulated in the largest markets immediately prior to the global financial crisis (GFC). While there is an element of truth in this contention, it betrays the more complex interactions between public legislators and influential transnational private trade associations, most notably the International Swaps and Derivatives Association (ISDA), both prior to the GFC and in the wake of it. ISDA, its members and national governments interact on the basis of legal and policy tradeoffs which are ostensibly related to OTC derivatives’ regulatory treatment but which, in reality, extend beyond this. The fact of these interactions between ISDA and nation states may raise less regulatory legitimacy challenges than some of the norms which are communicated. A prime example is the public transposition of ‘safe harbours’ which insulate OTC derivatives, including ‘purely speculative’ contracts, from the full force of gambling law. It is thus suggested that while the regulatory role and expertise of ISDA should be formally recognised and appropriately harnessed by public actors in the creation of a new public-private regulatory detente in the OTC derivatives markets, a review of the appropriateness of the current legal treatment of purely speculative derivatives should be a priority for any such regulatory regime.

Regulatory relationships in financial markets exemplify the importance and changing nature of transnational business governance interactions (TBGI). These interactions involve reciprocal forces of influence between private and public regulators. We examine one key case of private governance in financial markets: the emergence, structures and decision-making of Credit Derivatives Determinations Committees (DCs) of the International Swaps and Derivatives Association (ISDA). We highlight the mechanisms or ‘pathways’ of interaction between ISDA, governments, courts and public regulators. We demonstrate how interactions between state and non-state actors can occur in both operational and policy spheres. We find ISDA to be a particularly resilient private regulator in an environment subject both to the significant external shock of the Global Financial Crisis and intense pressure on governmental actors to demonstrate that they are counteracting risk. We consider the sources of ISDA’s adaptive capacities. It is clear that ISDA operates as a key gatekeeper in the field and, significantly, the organisation appears to have a form of 'regulatory licensing' power in the DCs. This power of regulatory licence is derived in an immediate sense from the propagation of a web of contracts and norms established by market actors, the content of which is substantially derived from instruments such as the Master Agreement, set down by ISDA itself. But, equally importantly, we find that this regulatory licensing capacity is ultimately backstopped by an implicit delegation from public actors, which lends additional legitimacy to the DCs. Deposited by bulk import

The functional reconstitution of Photosystem I reaction center cores by wild-type and mutant PsaC subunits at high ionic strength indicated that hydrophobic interactions are dominant in stabilizing...

We describe the insertion of an iron-sulfur center into a designed four alpha-helix model protein. The model protein was re-engineered by introducing four cysteine ligands required for the coordination of the mulinucleate cluster into positions in the main-chain directly analogous to the domain predicted to ligand the interpeptide [4Fe-4S (S-cys)4] cluster, Fx, from PsaA and PsaB of the Photosystem I reaction center. This was achieved by inserting the sequence, CDGPGRGGTC, which is conserved in PsaA and PsaB, into interhelical loops 1 and 3 of the four alpha-helix model. The holoprotein was characterized spectroscopically after insertion of the iron-sulfur center in vitro. EPR spectra confirmed the cluster is a [4Fe-4S] type, indicating that the cysteine thiolate ligands were positioned as designed. The midpoint potential of the iron-sulfur center in the model holoprotein was determined via redox titration and shown to be -422 mV (pH 8.3, n = 1). The results support proposals advanced for the structure of the domain of the [4Fe-4S] Fx cluster in Photosystem I based upon sequence predictions and molecular modeling. We suggest that the lower potential of the Fx cluster is most likely due to factors in the protein environment of Fx rather than the identity of the residues proximal to the coordinating ligands.

Regulatory relationships in financial markets exemplify the importance and changing nature of transnational business governance interactions (TBGI). These interactions involve reciprocal forces of influence between private and public regulators. This paper examines one key case of private governance in financial markets: the emergence, structures and decision-making of Credit Derivatives Determinations Committees (DCs) of the International Swaps and Derivatives Association (ISDA). The paper highlights the mechanisms or ‘pathways’ of interaction between ISDA, governments, courts and public regulators. Interactions between state and non-state actors are shown to occur in both operational and policy spheres. ISDA is found to be a particularly resilient private regulator in an environment subject both to the significant external shock of the global financial crisis and intense pressure on governmental actors to demonstrate that they are counteracting risk. The reasons behind ISDA’s adaptive capacities are considered.

We have postulated that the orientation of PsaC on the photosystem I core involves electrostatic interactions between charged residues on the core binding site and the subunit [Rodday, S. M., Jun, S.-S., & Biggins, J. (1993) Photosynth. Res. 36, 1-9]. We, therefore, changed eight acidic residues on PsaC to arginine and examined the efficiency of the mutant subunits in the reconstitution of P700-Fx cores in vitro. Reconstitution of the cores by the mutant subunits was determined by analysis of the kinetics of recombination reactions between P700+ and reduced acceptors as measured optically. Restoration of complete forward electron transfer, indicative of efficient subunit binding, was estimated from the ca. 30 ms decay component in the flash transients. Slightly reduced levels of reconstitution were observed for the mutants D24R, E46R/D47R. D61R, and E72R. In contrast, mutants D9R, E27R, and D32R showed significantly lower efficiencies. The presence of the iron-sulfur centers, FA and FB, in these three mutant subunits was confirmed by low-temperature EPR spectroscopy indicating that the polypeptides had folded correctly. We conclude that the introduction of positively charged side chains at positions 9, 27, and 32 seriously disrupts PsaC binding. However, when the wild-type acidic residues in these positions were changed to alanine, only mutant D9A showed a reduced level of reconstitution, suggesting that this aspartate is the most important residue participating in the electrostatic interaction with the core. The results are discussed in relation to the photosystem I crystal structure and support an orientation of PsaC on the core such that center FB is proximal to Fx.

The highly conserved amino acid sequence PCDGPGRGGTC in both photosystem I reaction center core proteins PsaA and PsaB has been predicted to contribute the four cysteine ligands for coordination of the 4Fe-4S iron-sulfur cluster FX, and we have proposed a working model for the binding of PsaC to this domain of the reaction center core heterodimer [Rodday et al. (1993) Photosynth. Res. 36, 1-9]. We have investigated structure-function relationships between this domain and the PsaC subunit by site-directed mutagenesis of the conserved prolines P560 and P564, and the charged residues D562 and R566 in the eucaryotic alga Chlamydomonas reinhardtii. The D562N and R566E mutants did not accumulate the PsaA and PsaB reaction center proteins, indicating that these residues are essential for the stable assembly of photosystem I. The P560A, P560L, and P564L mutants accumulated functional reaction centers but showed an impaired interaction between the reaction center core complex and the PsaC subunit. We observed that the reaction centers of the proline mutants dissociated more readily in urea, and reconstitution of the mutant core preparations using PsaC and Fe-S cluster insertion protocols in vitro were incomplete. We suggest that P560 and D562 contribute to the stability of the FX cluster, most likely by providing essential hydrogen bonding to the C561 ligand. The data obtained from the P564 and R566 replacements provide direct evidence that the intercysteinyl region in PsaB is a domain involved in the interaction between PsaC and the reaction center core.

John Biggins, BA, LL.M (Dub)—Research Associate, Centre for Regulation and Governance, University College Dublin. Catherine Donnelly, LL.B. (Dub)—B.C.L. (Oxon); LL.M. (Harv); D.Phil. (Oxon); Barrister, Blackstone Chambers, London, Law Library, Dublin; Attorney at Law, New York; Lecturer in Law, Trinity College, Dublin., latest update July 2011.The authors wish to thank the Department of Jobs, Enterprise and Innovation for helpful guidance regarding the transposition of the SD in Ireland. The views expressed herein are the authors’ alone and do not necessarily represent the views of any other individual or organisation. Errors and omissions also remain the authors’ alone.

It has frequently been claimed that over-the-counter (OTC) derivatives were, by and large, not directly regulated in the largest markets immediately prior to the global financial crisis (GFC). While there is an element of truth in this contention, it betrays the more complex interactions between public legislators and influential transnational private trade associations, most notably the International Swaps and Derivatives Association (ISDA), both prior to the GFC and in the wake of it. ISDA, its members and national governments interact on the basis of legal and policy tradeoffs which are ostensibly related to OTC derivatives' regulatory treatment but which, in reality, extend beyond this. The fact of these interactions between ISDA and nation states may raise less regulatory legitimacy challenges than some of the norms which are communicated. A prime example is the public transposition of ‘safe harbours’ which insulate OTC derivatives, including ‘purely speculative’ contracts, from the full force of gambling law. It is thus suggested that while the regulatory role and expertise of ISDA should be formally recognised and appropriately harnessed by public actors in the creation of a new public-private regulatory detente in the OTC derivatives markets, a review of the appropriateness of the current legal treatment of purely speculative derivatives should be a priority for any such regulatory regime.

Hyper- and hypo-osmotic salt shocks in the presence of [32P]PO43− led to the appearance and disappearance of several 32P-labelled proteins in vivo within a few minutes. Similar to the in vivo labelling experiments, a 20.5-kDa protein was also more intensely labelled in extracts from salt-shocked cells using [γ-32P]ATP in in vitro labelling experiments. Furthermore, labelling of this and a protein of about 64.4 kDa was induced by adding high amounts of NaCl directly to extracts of control cells in kinase assays. Therefore, changes in the NaCl contents led to alterations of the activity of protein in Synechocystis sp. PCC 6803, which may be involved in the signal transduction chain sensing changes in the NaCl content of the surrounding medium.

The structure of the predicted amino acid sequence in the FX domain of Photosystem 1 was studied by molecular modeling and a working hypothesis was developed for the functional interaction of PsaC with the core heterodimer. We propose that the intervening sequences between homologous cysteines in the FX cluster form two flexible loops and participate in the binding of PsaC, and that the arginine residues in the two surface-exposed loops may promote the interaction between the P700-FX core and the subunit. The model was tested experimentally; chemical modification of arginine residues in the P700-FX core using phenylglyoxal prevented reconstitution of the core with PsaC and PsaD after insertion of FeS clusters in vitro. Treatment of the P700-FX core with trypsin also prevented reconstitution of terminal electron transfer to FAFB, although neither treatments affected the electron transfer to FX as judged by flash kinetic spectrophotometry. Electron transfer in the P700-FAFB complex was not impaired by either phenylglyoxal or trypsin treatment indicating that the small subunit(s) protect the arginine residues that become chemically modified or cleaved. The data are consistent with the working model and point to additional experiments designed to identify the specific residues involved in the interaction between the P700-FX core and PsaC.

The electron spin polarized (ESP) electron paramagnetic resonance (EPR) signal observed in spinach Photosystem I (PS I) particles was examined in preparations depleted of vitamin K 1 by solvent extraction, followed by reconstitution with a series of quinones and quinone analogues. The ESP EPR signal was previously attributed to a radicalpair that included vitaim K 1 − (Rustandi, R.R., et al. (1990) Biochemistry 29, 8030–8032) and, in addition, vitamin K 1 was assigned as the secondary acceptor A 1 in PS I (Snyder, S.W., et al. (1991) Proc. Natl. Acad. Sci. USA, 88, 9895–9896). The ESP EPR signal was observed in untreated PS I preparations, was not detected in the solvent-extracted PS I samples and was restored upon reconstitution using certain quinones. The ability to restore the ESP EPR signal was dependent upon two properties of the reconstituted acceptor. First, the solution reduction potential of the reconstituted acceptor must be more positive than about −750 mV where the solution reduction potential of vitamin K 1 is −710 mV. Second, the structure of the reconstituted acceptor requires either a minimum of two aromatic rings (i.e., naphthoquinone) or a benzoquinone (or larger) derivative substituted with an alkyl tail. A model was developed to describe both the requirements for electron transfer to A 1 and also previous results for electron transfer from A 1 − to the iron-sulfur centers (Biggins, J. (1990) Biochemistry 29, 7259–7264). When untreated PS I preparations were incubated with perdeuterated vitamin K 1 (DK 1 ) the endogenous K 1 was observed to exchange with DK 1 . The replacement rate was strongly dependent upon temperature (h-days at 4°C, min at 37°C) and upon illumination (min). Naphthoquinones lacking a long alkyl tail were unable to exchange with endogenous vitamin K 1 . Although no known physiological role exists for vitamin K 1 ejection from its A 1 binding site, the quinone appears to be somewhat labile. Direct exchange of vitamin K 1 with exogenously supplied quinones indicates that the PS I A 1 site might be a target for the design of new herbicides in green plants.

Three physiological states brought about by different preillumination conditions in Ochromonas danica (state 1, state 2, and dark adapted) have been investigated using steady-state and time-resolved fluorescence at 77 K. The former reveals that the photosystem 1 (PS1) emission amplitude is the same in states 1 and 2. The photosystem 2 (PS2) emission amplitude depends on preillumination, state 1 having a higher peak than state 2 and dark adapted cells. Emission decay curves from PS1 are independent of preillumination, while decay curves from PS2 are identical for state-2 and dark adapted cells (1/e time 310 ps), state 1 showing a slower decay (1/e time 390 ps). No evidence suggests a preillumination-dependent redistribution of excitation energy from PS2 to PS1. Variation in the amplitude of a long-lifetime component appears to be sufficient to explain the state-dependent changes in emission of the PS2 peak. This is consistent with the hypothesis that some peripheral antenna is energetically decoupling without redistributing the excitation energy upon the state 2 to state 1 transition, causing increased emission in the 670–700 nm region.

This report describes the isolation and preliminary characterization of a new pigment-protein complex from the chromophyte alga, Ochromonas danica. The pigment-protein complex was obtained by extracting a thylakoid membrane preparation with the zwitterionic detergent lauryldimethylamine oxide followed by ultracentrifugation on sucrose gradients. The pigment-protein complex has been characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, absorption spectroscopy, and low temperature (77 Kelvin) chlorophyll fluorescence spectroscopy. A polypeptide with a monomeric molecular weight of 31,000 as determined by denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis was the major constituent of this pigment-protein complex. The major pigment in this complex was chlorophyll a, although an as yet unidentified carotenoid was also present. There was no evidence for the presence of chlorophyll c.

The phosphorylation of thylakoid membranes in the Chromophyte alga Ochromonas danica was studied in whole cells and in vitro. Protein kinase activity was observed in the thylakoid fraction, and several membrane-bound polypeptides were found to be phosphorylated. The thylakoid protein kinase demonstrated several unusual regulatory properties. Both the polypeptides that were phosphorylated and the rate of protein phosphorylation were independent of illumination. Protein kinase activity was also unaffected by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, diuron. The kinase activity was inhibited under strong reducing conditions. Whole cells labeled with (32)PO(4) (3-) were converted to light states I and II by pre-illumination favoring photosystem I or photosystem II, respectively. Analysis of the phosphoproteins from cells in state I and state II showed that no changes in phosphorylation accompanied the change in energy redistribution.

The South Australian government has recently formed a committee to investigate conflicts over the use of resources in the Mt. Lofty Ranges, including improvements to the quality of water supplied to the city of Adelaide. The committee is examining potential land-use and land-management policies. The writers have developed a prototype of a decision support system (DSS) that will estimate the effects of these policies on water quality and the costs of implementing the policies. The DSS consists of three modules. The policy module allows the user to build up a suite of policies in a formal syntax. The second module, the catchment model, will estimate the effects of these policies on total phosphorus, total nitrogen, and turbidity levels. The user can query the DSS about these estimates in the third module. The prototype has been evaluated by the South Australian Engineering and Water Supply Department, and a second version of the DSS is now being designed.

Selected substituted 1,4-benzoquinones, 1,4-naphthoquinones, and 9,10-anthraquinones were investigated as possible replacement quinones in spinach photosystem I (PSI) preparations that had been depleted of endogenous phylloquinone by extraction with hexane/methanol. As a criterion for successful biochemical reconstitution, the restoration of electron transfer was determined by measuring P-430 turnover at room temperature from flash-induced absorbance transients. Restoration of complete electron transfer between A0- and P-430 (terminal iron-sulfur centers, FAFB) was demonstrated by using phylloquinone, 2-methyl-3-decyl-1,4-naphthoquinone, 2-methyl-3-(isoprenyl)2-1,4-naphthoquinone, and 2-methyl-3-(isoprenyl)4-1,4-naphthoquinone. All other quinones tested did not restore P-430 turnover but acted as electron acceptors and oxidized A0-. It is concluded that the specificity of the replacement quinone for interaction with the primary acceptor, A0-, is low but additional structural constraints are required for the quinone occupying the A1 site to donate to the iron-sulfur center, Fx. It is suggested that the 3-phytyl side chain of phylloquinone and the 3-alkyl tails of the three naphthoquinones that restored P-430 turnover may be required for interaction with a hydrophobic domain of the A1 site in the PSI core to promote electron transfer to Fx and then to FAFB.

The electron spin polarized (ESP) electron paramagnetic resonance (EPR) signal observed in spinach photosystem I (PSI) particles was examined in preparations depleted of vitamin K1 by solvent extraction and following biological reconstitution by the quinone. The ESP EPR signal was not detected in the solvent-extracted PSI sample but was restored upon reconstitution with either protonated or deuterated vitamin K1 under conditions that also restored electron transfer to the terminal PSI acceptors. Reconstitution using deuterated vitamin K1 resulted in a line narrowing of the ESP EPR signal, supporting the conclusion that the ESP EPR signals in the reconstituted samples arise from a radical pair consisting of the oxidized PSI primary donor, P700+, and reduced vitamin K1.

The interaction of PsaC with the core heterodimer of Photosystem 1 was studied in wild type Synechocystis sp. PCC 6803 and the site-directed mutant R561E of PsaB. The mutant reaction center was much less stable in urea and the functional reconstitution of the mutant core using PsaC was impaired. However, the extent of reconstitution increased in the presence of divalent cations whereas that of the wild type was inhibited. We conclude that the reaction center in the mutant is unstable, most likely due to the introduction of an unfavorable electrostatic interaction between surface-exposed residues on PsaC and the binding site for the subunit on the core heterodimer in support of the model proposed previously (Rodday et al. (1993) Photosynth Res 36: 1–9).

The green sulfur bacterium Chlorobium vibrioforme was cultured in the presence of ethylene to selectively inhibit the synthesis of the chlorosome antenna BChl d. Use of these cells as starting material simplified the isolation of a photoactive antenna-depleted membrane fraction without the use of high concentrations of detergents. The preparation had a BChl alpha/P840 of 50, and the spectral properties were similar to those of preparations isolated from cells grown with a normal complement of chlorosomes. The membrane preparation was active in NADP+ photoreduction. This indicated that the fraction contained reaction centers with complete electron-transfer sequences which were then characterized further by flash kinetic spectrophotometry and EPR. We confirmed that cytochrome c553 is the endogenous donor to P840+, and at room temperature we observed a recombination reaction between the reduced terminal acceptor and P840+ with a t1/2 = 7 ms. Oxidative degradation of iron-sulfur centers using low concentrations of chaotropic salts introduced a faster recombination reaction of t1/2 = 50 microseconds which was lost at higher concentrations of chaotrope, indicating the participation of another iron-sulfur redox center earlier than the terminal acceptor. Cluster insertion using ferric chloride and sodium sulfide in the presence of 2-mercaptoethanol restored both the 50-microseconds and 7-ms recombination reactions, allowing definitive assignments of these centers as iron-sulfur centers. Following the suggestion of Nitschke et al. [(1990) Biochemistry 29, 3834-3842], we associate these two kinetic phases to back-reactions between P840+ and iron-sulfur centers FX and FAFB, respectively. The iron-sulfur cluster degradation and reconstitution protocols also led to inhibition and restoration of NADP+ photoreduction by the membrane preparation, providing unequivocal evidence for the function of the centers FX and FAFB in the physiological electron-transfer sequence on the acceptor side of the Chlorobium reaction center. At 77 K we observed a recombination reaction of t1/2 = 20 ms that we suggest occurs between Fx- and P840+. Degradation of the iron-sulfur clusters resulted in replacement of the 20-ms phase with a faster reaction of t1/2 = 80 microseconds that was most likely a recombination between the early acceptor A1- and P840+ or decay of 3P840. Analysis of the iron-sulfur centers in the preparation by EPR at cryogenic temperature supports the optical measurements. EPR signals originating from the terminal acceptor(s) were not observed following treatment of the membrane preparation by chaotropes, and a modified signal was restored following cluster reinsertion.(ABSTRACT TRUNCATED AT 400 WORDS)

The characteristic electron spin polarized electron paramagnetic resonance (ESP EPR) signal observed in photosystem I (PSI) has been previously assigned to a radical pair composed of the oxidized primary donor and a reduced vitamin K1. Under conditions in which Bottin, H. & Setif, P. [(1991), Biochim. Biophys. Acta 105, 331-336] proposed that A1 is doubly reduced, the ESP EPR signal was not observed. Therefore, the ESP EPR signal can be directly attributed to A-1, and vitamin K1 can be assigned as this PSI acceptor. The ESP EPR signal was partially restored by removal of the chemical reductants.

The stabilization of charge in the primary reaction of PSI is promoted by rapid electron transfer reactions involving the five redox centers A0A1FxFAFB (1). A0 is monomelic Chl a and FxFAFB are 4Fe:4S clusters. FX is associated with the PSI core and FAFB are localized on an 8·9 kDa polypeptide. Provisional identification of A1 as a quinone was based upon the EPR signal of A1 (2,3) and comparison of the electron spin polarized flash-induced EPR K-band spectrum of the species P700+A1 - with that of P870 +Q- in Fe-depleted bacterial reaction centers (4). Direct support for the participation of quinone followed a study of flash-induced optical transients at low temperature (5) and the specific reconstitution of room temperature electron transfer reactions in solvent-extracted cyanobacterial PSI using phylloquinone (vitamin K1) (6). The reconstitution studies have been recently confirmed using an ether-extracted preparation of PSI derived from spinach (7).

Mechanisms for the regulation of excitation energy distribution between PS2 and PS1 have been proposed for higher plants (mobile antenna hypothesis) and for red algae cyanobacteria (spillover). These organisms utilize Chl b and phycobilins respectively as accessory light harvesting pigments. The Chromophytic algae encompass a taxonomically diverse group of phyla which are very successful competitors and contribute substantially to net global photosynthesis. These algae are characterized by their use of Chl c and carotenoid (fucoxanthin or peridinin) as accessory light harvesting pigments and by the arrangement of their thylakoids into extended bands of three. Despite their obvious importance, there has only been one prior report on the regulation of energy transfer in Chromophytic algae in which Owens (1) reported only intensity dependent changes. We have previously shown that the Chromophyte Ochromonas danica shows wavelength dependent changes in chlorophyll fluorescence (both 77K and room temperature) which are diagnostic for a re-distribution of excitation energy (2). We report here on the antenna polypeptide composition of O. danica as well as the in vitro protein kinase activity.

The kinetics of photooxidation and reduction of cytochrome f were examined spectrophotometrically in the red alga Porphyridium cruentum in light State 1 and light State 2. Experiments were performed on intact cells that had been chemically fixed and stabilized in the light states. The cytochrome f turnover was measured during conditions of linear electron transport driven by both photosystems and during several cyclic reactions mediated by the long-wavelength Photosystem (PS) I. The data show that the rate of photooxidation of cytochrome f increased in State 2 when the cells were activated by subsaturating intensities of green light absorbed primarily by the phycobilisome. No differences in kinetics were found between algae in State 1 or State 2 when they were activated by light absorbed primarily by the chlorophyll of PS I. The results confirm that changes in energy distribution between the two photosystems occur as a result of the light state transition and verify that the redistribution of excitation results in the predicted changes in electron transport.

We have studied the redistribution of excitation energy in the cryptomonad alga Cryptomonas ovata . Low-temperature fluorescence emission spectra from cells preilluminated with light 1 and light 2 show that preferential excitation of Photosystem II (PS II) leads to decreased fluorescence emission from chlorophyll (Chl) a associated with PS II relative to the emission following the preferential excitation of Photosystem I (PS I). The fluorescence change is indicative of a light-state transition by the cells. However, comparision of measurements of the kinetics of P-700 photooxidation by cells fixed with glutaraldehyde following illumination with light 1 or light 2 shows that the relative activity of PS I is lower in cells fixed in light 2. This is in contrast to the expectation for cells in State 2. Excitation spectra for the fluorescence emission from PS II Chl a show that preferential excitation of PS II leads to a decreased probability for energy transfer from phycoerythrin and Chl c 2 to PS II when compared to cells in which PS I is preferentially excited. This result is in accordance with recent picosecond time-resolved fluorescence studies (Bruce, D., Biggins, J., Charbonneau, S. and Thewalt, M. (1987) in Progress in Photosynthesis Research (Biggins, J., ed.), Vol. II, pp. 777–780, Martinus Nijhoff, Dordrecht) and we, therefore, suggest that C. ovata does not undergo a classical light-state transition. However, preferential excitation of PS II or PS I appears to cause pigment-protein conformational changes which change the probability for energy transfer from phycoerythrin to PS II, and we suggest that this may be a mechanism for photoprotection of PS II. Studies of the kinetics of excitation-energy redistribution, and of the effects of electron-transport inhibitors and uncouplers of photophosphorylation indicate that the mechanism for excitation-energy redistribution in C. ovata and phycobilisome-containing organisms may be similar.

Excitation energy distribution in Porphyridium cruentum in state 1 and state 2 was investigated by time resolved 77 K fluorescence emission spectroscopy. The fluorescence rise times of phycoerythrin, phycocyanin and allophycocyanin (in cells in state 1 and state 2) were very similar in contrast to the emission from chlorophyll a (Chl a) associated with the two photosystems. In state 2 photosystem II (PSII) Chl a fluorescence emission rose faster than the PSI Chl a emission and decayed more rapidly, and the converse was observed in state 1. These kinetic data support the concept of increased energy transfer from PSII Chl a to PSI Chl a in state 2 in P. cruentum.

The light-induced turnover of P700 was measured spectrophotometrically in a wide variety of algae and some photosynthetic mutants. Analysis of the postillumination recovery of P700+ revealed that the apparent first-order rate constant for reduction via the cyclic pathway was much lower that that via the noncyclic pathway. After activation of photosystems 1 and 2 the half-time for reduction of P700+ was 5-20 ms, whereas after activation of primarily photosystem 1 a longer half-time of ca. 150 ms was observed. The extent of the photooxidation of P700 was the same in both regimes of illumination. The longer half-time was also noted after inhibition of photosystem 2 by 3-(3,4-dichlorophenyl)-1,1-dimethylurea or mild heat shock and in mutant algae known to lack a functional photosystem 2. No signal was observed in mutants lacking P700 itself but those strains lacking either plastocyanin or cytochrome f were capable of a very slow turnover (reduction t 1/2 greater than 500 ms at room temperature). This very slow turnover was not affected by carbonyl cyanide m-chlorophenylhydrazone or the plastoquinone antagonist, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, indicating that the pathway for reduction of P700+ in these mutants is not energy linked and does not utilize the intersystem electron transport chain. The slow, 150 ms, reduction of P700+ due to cyclic flow was not observed when cells were engaged in photosynthesis at high-light intensities. The data are interpreted as evidence for the involvement of the total functional pool of P700 in both electron transport pathways, and we suggest that cyclic electron transport does not contribute to photosynthesis in oxygen-evolving autotrophs.

Excitation spectra of chlorophyll-a (Chl-a) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl-a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl-a (445 nm) as compared to excitation spectra for emission from Chl-a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl-c2 to PSII Chl-a fluorescence emission. In all three species the absorbance band positions of Chl-a, as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome-containing organisms. Time-resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl-c2, PSII Chl-a, and PSI Chl-a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl-a, and PSI Chl-a. Spectral red-shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae.

Photosystem I preparations were irradiated with UV to destroy vitamin K1 in situ. The depletion of vitamin K1 resulted in inactivation of NADP+ photoreduction and introduction of a approximately 220 ms component in the flash generated P700+ rereduction at room temperature. The photoreduction of the terminal FeS centers FA and FB in control and vitamin K1-depleted preparations at 7 K were comparable. The data confirm that vitamin K1 is functionally implicated in primary electron transfer reactions in PS I at physiological temperature, and that the anomalous results at cryogenic temperature may be explicable in terms of a by-pass of the vitamin K1 acceptor site or heterogeneity introduced into the photosystem by quinone removal.

Linear-dichroism spectra of Anacystis nidulans at 77 K were determined for whole cells chemically fixed in light State 1 and light State 2. Whole cells were oriented by the squeezed gel technique using 5% gelatin 2.2 M sucrose gels. Peaks with positive dichroism were observed at 638 nm and 688 nm with shoulders at approx. 650 nm and 700 nm. The amplitude of the 650 nm shoulder was greater for cells in State 2 than those in State 1, and the State-2-minus-State 1 difference spectrum had a single peak at 656 nm. The linear dichroism spectrum of phycobilisomes isolated from A. nidulans showed peaks at 635 nm (phycocyanin) and 656 nm (allophycocyanin). The spectrum for thylakoid membranes free of phycobilisomes had one peak at 685 nm with a shoulder at 698 nm. We suggest that the change in dichroism at 656 nm between cells in State 1 and State 2 results from a change in orientation of the allophycocyanin core of the phycobilisome. This result is discussed in the context of our model for the light-state transition in phycobilisome-containing organisms.

A commercially available CaMoO4 tunable acousto‐optic filter has been evaluated for use as a monochromator and modulator for incorporation into a rapid scanning spectrophotometer for the wavelength range 450–750 nm. The construction of a suitable rf driver is described. The bandwidth of light transmitted by the filter was found to be between 2 and 6 A, permitting excellent spectral resolution. The contrast ratio was greater than 1400 over the major portion of the tuning range, and the skirt rejection was 35–40 dB for 1‐nm‐wide bands 10–100 nm distant from the center wavelength. The transmission of the filter can be switched in 20 μsec, and modulation frequencies up to 25 kHz are attainable without appreciable loss of transmission. With a conventional light source the output intensity of monochromatic light is comparable to grating monochromators. Stray light can be effectively compensated for by transmission modulation and phase‐sensitive detection of the output. We show that the use of the filter as a monochromator is in many respects superior to the other devices which have been used previously for rapid scanning. The filter may also be used as a light modulator or multiple‐beam spectrophotometer and, by virture of its electronic control and ease of interfacing with digital computers, can be considered to be a programmable light source.

A chlorophyll a, c-fucoxanthin pigment-protein complex8 functions as the major light harvesting antenna in the Chrysophyte Ochromonas danica. The regulated distribution of excitation energy between the two photosystems was investigated in these organisms and was shown to be strongly wavelength dependent. A light state transition was induced by pre-illumination of cells using light 2 (640 nm) and light 1 (700 nm) of equal absorbed intensity, and detected by reversible changes in the 77 K chlorophyll fluorescence emission spectra. Peaks at ∼ 690 nm and ∼ 720 nm in the low temperature spectra are most likely associated with PS2 and PS1 respectively. A room temperature fluorescence emission at 680 nm induced by modulated light 2 (500 nm) was strongly quenched in the presence of background light 1 (720 nm). Removal of light 1 led to an increase in fluorescence followed by a slow quenching. The room temperature fluorescence changes were directly correlated with changes in the 77 K emission spectra that indicated a change in the distribution of excitation energy between the two photosystems. It was established that DCMU (1 μmol) prevented the state 2. The conversion to state 1 followed a simple photochemical dose dependence and had a half-time of 20 s-1.5 min at 6 W m(-2). In contrast, the conversion to state 2 was independent of light intensity. These data indicate that O. danica undergoes a light state transition in response to the preferential excitation of PS2 or PS1.

The kinetics of P -700 were examined spectrophotometrically during the induction of photosynthesis in algae. A pronounced oscillation was observed in the redox level of P -700 upon illumination of dark-adapted cells. The dark adaptation required approximately 1 min. The oscillation may be described as an initial rapid oxidation reaching a peak at approx. 50 ms followed by complete reduction of the pool of P -700. A subsequent slower oxidation resulted in attainment of the final state around 1 s. The main features of the oscillation were qualitatively the same in a wide variety of algae. The modulation in redox level of P -700 required high intensity activation of both photosystems and was eliminated by pre-illumination of the cells with weak short wavelength light but not by longer wavelengths absorbed primarily by Photosystem I. We propose that the P -700 modulation is directly related to the fast redox changes in Photosystem II which occur during the induction of photosynthesis. Cells incubated with methyl viologen did not show the P -700 oscillation confirming the suggestion previously advanced that exhaustion of Photosystem I acceptor and kinetic limitations in the carbon reduction cycle partially control the fast phase of photosynthetic induction.

The function of vitamin K1 in the primary electron-transfer processes of photosystem I (PS I) was investigated in the cyanobacterium Synechocystis 6803. A preparation of purified PS I was found to contain two vitamin K1's per reaction center. One vitamin K1 was removed by extraction with hexane, and further extraction using hexane including 0.3% methanol resulted in a preparation devoid of vitamin K1. The hexane-extracted PS I was functional in the photoreduction of NADP+, but the PS I after extraction using hexane-methanol was totally inactive. Activity was restored by using exogenous vitamin K1 plus the hexane extract. Vitamin K3 would not substitute. The room temperature recombination kinetics of the PS I extracted with hexane were not significantly modified. However, following the removal of both vitamin K1's, the 20-ms recombination between P-700+ and P-430- was replaced by a dominant relaxation (t 1/2 = 30 ns) due to recombination of the primary biradical P-700+ A0- and a slower component originating from the P-700 triplet. This kinetic behavior was consistent with an interruption of forward electron transfer to the acceptor A1. Addition of either vitamin K1 or vitamin K3 to such preparations resulted in restoration of the slow kinetic phase (greater than 2 ms), indicating significant competition by the two exogenous quinones for electron transfer from A0-. In the case of vitamin K3, this change in the kinetics induced by vitamin K1, suggesting successful reconstitution of the acceptor site A1. These data support the hypothesis that acceptor A1 is vitamin K1 and is a component of the electron-transfer pathway for NADP+ reduction.

The effect of reversible membrane phosphorylation on the room temperature linear dichroism signal of magneto-oriented pea thylakoids was investigated. Membrane phosphorylation, induced by photoreduction of the plastoquinone pool, resulted in a change in the linear dichroism signal in the region of the red absorption band of chlorophyll. The optical change was due to modifications in selective polarized light scattering which have been shown to be indicative of alterations in the degree of membrane stacking. No changes in linear dichroism due to a reorientation of pigments were observed. It is concluded that phosphorylation of the membrane results in about a 10% destacking of the thylakoids and that this conformational change is implicated in energy redistribution between the two photosystems.

The possible involvement of a reversible protein phosphorylation event in the regulation of excitation energy distribution was studied in the red alga Porphyridium cruentum. Whole cells were incubated in phosphate-depleted growth medium containing carrier-free [32P]orthophosphate for several hours to label the intracellular phosphate pools, and they were then converted to State 1 or State 2 by illumination using blue or green light, respectively. The successful transition to State 1 or State 2 was verified by 77 K fluorescence spectroscopy of the chlorophyll emission and the cells were then denatured using either acetone, trichloroacetic acid or boiling detergent. The whole cell lysates were solubilized, treated with RNAase, and analyzed for phosphoproteins by SDS-polyacrylamide gel electrophoresis. At least twelve polypeptides were found to be phosphorylated but no changes in specific radioactivity of the polypeptides were detected when samples from cells in State 1 and State 2 were compared. We conclude that a reversible protein phosphorylation event is not implicated in the state transition in P. cruentum. A model is presented for the mechanism of the light state transition in organisms that contain phycobilisomes which is different from the mechanism of energy distribution proposed for higher plants.

The assimilation of CO 2 by etiolated Hordeum vulgare seedlings during an illumination period indicates a conversion of the organisms to autotrophy. After 1 hour illumination, increases in the photo-assimilation of CO 2 are observed and the distribution of C 14 in the soluble fraction of the plants is predominantly in intermediates of the Calvin cycle.

Particles from both Saprospira grandis and Vitreoscilla species, obtained by high-pressure extrusion and sonic treatment, respectively, actively catalyze the oxidation of reduced nicotinamide adenine dinucleotide (NADH) and succinate with O 2 . These activities are inhibited by cyanide but not by antimycin; Saprospira is also amytal- and rotenone-insensitive. Vitreoscilla preparations were unable to oxidize mammalian ferrocytochrome c and reduced tetramethyl- p -phenylenediamine, whereas the Saprospira preparations did so actively. Low-temperature (77 K) difference spectroscopy of Vitreoscilla cells and particles indicates the presence of three maxima in the cytochrome alpha-region at 554, 558, and 562 nm. All three cytochromes are active in NADH and succinate oxidation, but none is ascorbate reducible. Cytochrome o is the only CO-binding pigment present and is probably the terminal oxidase; it has properties similar to the cytochrome o isolated in solubilized form from this organism. Saprospira cells and membranes exhibit four cytochrome absorption bands whose maxima are at 550, 554, 558, and 603 nm at 77 K. The latter component has not been noted previously. NADH and succinate reduce all four cytochromes, but ascorbate reduces only the 550- and 603-nm pigments. CO spectra indicate the presence of cytochrome a,a 3 which is probably the oxidase. A second CO-binding pigment is present which is not a peroxidase but may be a cytochrome.

The association of the photo-induced electron paramagnetic resonance signal in photosynthetic tissue with the necessity for the presence of chlorophyll is demonstrated with a variety of mutant organisms. This is taken as additional evidence of the direct electron-transfer reaction from and/or to chlorophyll as the primary quantum conversion step.

Membrane fragments from the marine flexibacterium Leucothrix mucor can be obtained by disrupting the cells by sonication or high-pressure extrusion. Such preparations are active in the oxidation of NADH and succinate and are inhibited by antimycin A, HOQNO, cyanide, and CO. The antimycin inhibition can be bypassed by TMPD. NADH-oxidase is not inhibited by rotenone or amytal. The particles can also interact in oxidative activities with DPIP, PMS, ferricyanide, ascorbate, and mammalian cytochrome c . Low-temperature (−196 °) difference spectrophotometry of whole cells and particles reveals the presence of four absorption bands in the α region of cytochromes, the relative absorbencies of which are markedly affected by growth conditions of the cells. From observations on the steady-state level of reduction of these components in the presence of various substrates, reductants, and inhibitors, we propose that the sequence of electron carriers is: substrate→ B 562 → C 552(458) → B 558 → oxygen. The only CO-binding pigment present in this organism is photodissociable at room temperature but not at −196 ° and is spectroscopically similar to cytochrome o . We suggest that this pigment is the functional terminal oxidase in L. mucor and is equivalent to cytochrome B 558 .