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It is now well established that the source of oxygen in photosynthesis is water. The earliest suggestion previously known to us had come from René Bernard Wurmser (1930). Here, we highlight an earlier report by Monsieur De Fourcroy (1787), who had already discussed the broad outlines of such a hypothesis in a book on Chemistry written for women. We present here a free translation of a passage from this book, with the original text in French as an Appendix.

Research has been conducted on antimycin-treated chromophores from Rodobacter sphaeroides. Results demonstrate that addition of myxothiazol to these chromophores at ambient redox potentials increases flash-induced oxidation of cytochrome c (sub)1.

Research examines the antimycin A- and/or myxothiazol-resistant reduction of cytochrome c with respect to side reactions, during Q-cycle catalysis, involving reduction of oxygen by the Q(sub)o site semiquinone, in isolated yeast cytochrome bc(sub)1 complex under both aerobic and anaerobic conditions.

Results show that the electrogenic reactions of the cytochrome bc(sup)1 complex are influenced by the transmembrane electric field produced by the reaction center of Rhodobacter sphaeroides. Data indicate that a reversal of electron transfer between b(sub)1 and b(sub)H hemes is a result of redox reactions associated with the b(sub)H heme.

Results show that Rhodobacter sphaeroides chromatophores are modified by N,N'-dicyclohexylcarbodiimide with changes in the rate of Q(sub)0H(sub)2 oxidation by the iron-sulfur protein.

Examination of the electrogenic and electron-transfer activities of the cytochrome bc1 complex in chromatophores from wild and mutant Rhodobacter sphaeroides bacteria, in which the cytochrome b aspartate-187 substitutes for asparagine, no difference in the inhibition patern by N,N'-dicyclohexylcarbodiimide is observed suggesting that aspartate-187 has no role in the protonogenic reaction.

Specific mutagenesis of the Rieske iron-sulfur protein in Rhodobacter sphaeroides is discussed. It shows that the thermodynamic gradient and the pK of the oxidized form determine the rate of quinol oxidation by the bc(sub.1) complex. Four mutant strains of Rb. sphaeroides were generated. In these strains Tyr 156 was mutated to Leu, His, Trp or Phe. The bc(sub.1) complex was put together and was able to support photosynthetic growth in mutants.

The movement of the iron sulfur subunit of mitochondrial ubihydroquinone:cytochrome c oxidoreductase is not responsible for the activation barrier associated with quinol oxidation. The activation energies of the reactions causing the movement are lower than the barrier.

The Q(sub)o site of mitochondrial ubihydroquinone:cytochrome C oxidoreductase can contain only an inhibitor or a quinol but not both. The exit tunnel forces the hydrophobic tails of compounds to occupy the same space. Therefore one would be displaced by the other.

The [2Fe-2S] cluster in ubihydroquinone:cytochrome c oxidoreductase rotates so the same docking surface interacts with cytochrome c(sub)1 and cytochrome b. The rotation occurs via an extension of a helical segment in the short linking span.

A study was conducted to characterize two novel properties of cytochrome b6f complexes by altering the cytochrome b subunit of the cytochrome bc1 complex from Rhodobacter spaeroides. Site-directed mutagenesis was carried out using polymerase chain reaction techniques. Results indicated that threonine had little effect on protein folding or assembly. Findings also showed that the complementation between two fragments of a split cytochrome b supported a final conformation that accommodated rapid electron transfers through the mutant bc1 complex.

The role of isocytochrome type c2 (isocyt c2) in photosynthetic electron transfer chain involved in the transduction of light into biological energy was studied using kinetic assay. The isocyt c2 exhibited significantly lower affinity for RC complexes than is expected of the members of the cyt c2 family. It also appeared to limit the rate of P280+ reduction. These activities can be attributed to the sequence, structural and conformational properties of the cytochrome.

Site-directed mutagenesis of the highly conserved tryptophan-129 and arginine-14 residues in cytochrome b subunit of Rhodobacter sphaeroides bc1 complex reveals that the two residues are vital for the stability and structure of the bc1 complex. Mutations affect the quinone reductase site, cytochromes bH and bL and the photosynthetic development of R. sphaeroides. The functions of the two residues are in agreement with the positions of the residues close to the cytoplasmic sides of the putative transmembrane helices C and B.

The area binding the 2Fe-2S group of the Rieske subunit of the ubiquinol:cytochrome C2 oxidoreductase of Rhodobacter sphaeroides, is found in site-directed mutations of conserved residues. Glycine is replaced with aspartate to analyze the thermodynamic reaction and the kinetics of ubiquinol:cytochrome C2 oxidoreductase on flash activation of the photosynthetic chain. The quinol oxidizing site shows the presence of the impaired catalyst in the mutant complex. The cytochrome subunit does not affect the basic structure of the 2Fe-2S group.

The effect of site-specific mutations on the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides was investigated. Mutation was aimed at the residues which were in proximity to the quinone reductase site. REsults indicated that the mutants maintained a functional quinol oxidizing site although the rate of cytochrome bh reoxidation was variably affected. A critical defect was observed in the bc1 complex due to deficient reoxidation of cytochrome bh by ubiquinone. This in turn, impedes electron transport through the cytochromes.

The construction and characterization of Escherichia coli and Rhodobacter sphaeroides strains which express the entire Rieske iron-sulfur subunit of the R. sphaeroides cytochrome bc1 complex and of E. coli strains which express subdomains of the subunit were reported. The study showed that the cytochrome b or c1 subunits are not required for mebrane-binding or for assembly of the iron-sulfur subuunit, although they are needed for stability ofthe subunit.

The presence of two different types of proteins with distinct biological electron-transfer functions is reflected in the redox potential (Em) cluster, and its pH dependence. A comparative study of the pH-dependent RR spectral changes, of three Rieske-type [2Fe-2S] proteins with different redox properties, is presented.

The use of protein-film voltammetry (PFV) is described to compare the redox behavior of three different Rieske proteins, RsRp, TtRp and BphF. The importance of the coupling between oxidation state and histidine protonation state is used to determine reduction potentials of Rieske clusters.