title: The photoreduction of nicotinamide-adenine dinucleotide by chromatophore fractions from Rhodospirillum rubrum.
abstract: The photoreduction of nicotinamide-adenine dinucleotide (NAD(+)), catalyzed by chromatophore fractions from young (1 day) and old (4-5 days) cultures of Rhodospirillum rubrum, was measured in the presence of either succinate or 2,6-dichlorophenol indophenol (DPIP) and an excess of ascorbate. The time-course of photoreduction in the succinate system suggested a "reversed electron flow" from the donor to NAD(+) mediated by a high energy intermediate produced by a light-induced, cyclic electron transport in the chromatophore fractions. The effects of the uncoupler carbonyl cyanide [p-(trifluoromethoxy)phenyl]hydrazone (FCCP) and of the inhibitors antimycin A and 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) were consistent with this interpretation. The time-course of NAD(+) photoreduction in the presence of DPIP and ascorbate suggested a direct, light-induced electron transport from the donor to the acceptor. We cannot yet distinguish between a model in which the same reaction center is utilized in the photoreduction by both donor systems (the reaction center component P-870 may relate to two primary acceptors at different redox potential levels) and a model in which each photoreducing system is driven by its own reaction center component.
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D020130:Bacterial Chromatophores / Q000378:metabolism*; D003486:Cyanides / Q000494:pharmacology; D005650:Fumarates / Q000378:metabolism; D006835:Hydrazones / Q000494:pharmacology; D007215:Indophenol / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D009243:NAD / Q000378:metabolism / Q000528:radiation effects*; D010084:Oxidation-Reduction; D010636:Phenols / Q000378:metabolism; D010777:Photochemistry; D011804:Quinolines / Q000494:pharmacology; D012246:Rhodospirillum / Q000378:metabolism*; D012247:Rhodospirillum rubrum / Q000378:metabolism; D013386:Succinates / Q000378:metabolism
chemical_list: D003486:Cyanides; D005650:Fumarates; D006835:Hydrazones; D010636:Phenols; D011804:Quinolines; D013386:Succinates; D009243:NAD; D007215:Indophenol; D000968:Antimycin A