title: Light inhibition of respiration is due to a dual function of the cytochrome b6-f complex and the plastocyanin/cytochrome c-553 pool in Aphanocapsa.
abstract: Studies of the respiratory electron transport pathway in the blue-green alga, Aphanocapsa, demonstrated the presence of cytochrome oxidase and a cytochrome complex. The use of antimycin A showed only the occurrence of a plastidal type of cytochrome complex (the cytochrome b6-f complex), which is insensitive to this inhibitor. Determination of the extent of photooxidation of cytochromes c-553 and f-556 under conditions of high and low cytochrome oxidase activities indicated an electron flow through both cytochromes to cytochrome oxidase. Direct evidence for a common segment of photosynthetic and respiratory electron transport from plastoquinone via the cytochrome b6-f complex to the soluble plastocyanin/cytochrome c-553 pool, as well as a competition between cytochrome oxidase and Photosystem I for reductants in this pool in the light, was obtained by measurements of electron transport with suitable electron donors in this alga.
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D045348:Cytochromes f; D004579:Electron Transport / Q000528:radiation effects; D003576:Electron Transport Complex IV / Q000378:metabolism; D008027:Light; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010101:Oxygen Consumption; D010788:Photosynthesis; D010940:Plant Proteins / Q000378:metabolism*; D010970:Plastocyanin / Q000378:metabolism*
chemical_list: D003574:Cytochrome c Group; D003580:Cytochromes; D010940:Plant Proteins; C083951:cytochrome c553; D009243:NAD; D009249:NADP; D010970:Plastocyanin; D045348:Cytochromes f; C022302:cytochrome C-552; D003576:Electron Transport Complex IV