title: Photoreactions of cytochromes in algal chloroplasts.
abstract: Light-induced cytochrome redox reactions were investigated with algal chloroplasts capable of high rates of electron transport coupled to phosphorylation. The electron-donor pool preceding photosystem I consists of membrane-bound cytochrome f-554.5 and a soluble cytochrome c-553; the latter replaces the function of plastocyanin of higher-plant chloroplasts. Both cytochromes are reduced by photosystem II and oxidized by photosystem I. A site of energy conservation precedes these c-type cytochromes. The data obtained with respect to the function of b-type cytochromes are comparable to those obtained with higher-plant chloroplasts. Cyclic electron transport is mediated by cytochrome b-563 in a photosystem-I-dependent reaction. In addition, cytochrome b-563 may be reduced by photosystem II, in accordance with recent findings with intact spinach chloroplasts. It therefore appears that cytochrome b-563 is a member of both cyclic and non-cyclic electron transport. In contrast to higher-plant chloroplasts, redox reactions of cytochrome b-559 are observable without any pretreatments. Cytochrome b-559, high-potential, is reduced by photosystem II through plastoquinone. In the presence of carbonyl cyanide m-chlorophenylhydrazone a cytochrome-b-559 oxidation by photosystem II is measured.
mesh_terms: D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002736:Chloroplasts / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism / Q000528:radiation effects*; D003991:Dibromothymoquinone / Q000494:pharmacology; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D056890:Eukaryota / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D013053:Spectrophotometry
chemical_list: D003580:Cytochromes; D003991:Dibromothymoquinone; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D004237:Diuron