Studies of proteins involved in photosynthesis point to an important pathway of fermentation which permits survival of cyanobacteria and algae under dark, anaerobic conditions. Studies of the soluble, low potential cytochrome c which is abundant in some cyanobacteria and algae suggest that this cytochrome links ferredoxin to hydrogenase in supporting the fermentation of carbohydrate reserves. The hypothesis of cytochrome function to be tested is based on data from enzymology and cell physiology. It must be confirmed by the techniques of gene deletion. Studies of the chemistry of catalyst interaction and of regulation of expression of the genes involved are proposed. Different sets of catalysts of this pathway were present in different compartments of the cell. The structure and function of these proteins will be studied. There is evidence that a carotenoid protein may function to protect cyanobacteria from photodestruction in bright light. Experiments are proposed to extend and clarify this hypothesis. Cytochrome c6 may be a catalyst of both photosynthetic and respiratory electron transport. We have found three isoforms of this catalyst. The PI will study the chemical basis for these forms and look for roles in distinct catalytic functions or in targeting to different compartments of the cell.
