title: The photosynthetic electron transfer chain of Chromatium vinosum chromatophores: flash-induced cytochrome b reduction.
abstract: Reduction of a cytochrome b following excitation by a single, short, near-saturating light flash has been demonstrated in Chromatium vinosum chromatophores. The extent of reduction is increased by addition of antimycin. The cytochrome has an alpha-band maximum at 562 nm in the presence of antimycin. The cytochrome b reduction is most readily observed in the presence of antimycin at high redox potential when cytochrome c-555 is oxidised before excitation. Under these conditions the half-time for reduction is about 20 ms, and the extent is about 0.5 mol of cytochrome b reduced per mol of reaction center oxidised. This extent of reduction is observed on the first flash-excitation from the dark-adapted state, and there was no indication that the reaction center quinone acceptor complex acted as a two-electron accumulating system. With cytochrome c-555 reduced before excitation, the extent of cytochrome b reduction is approximately halved. The factors which result in substoichiometric cytochrome b reduction are not yet understood. Agents which appear to inhibit primary acceptor oxidation by the secondary acceptor (UHDBT, PHDBT, DDAQQ, HOQNO, o-phenanthroline), inhibit reduction of the cytochrome b. DBMIB inhibits cytochrome b reduction but does not appear to inhibit primary acceptor oxidation. These observations confirm that a cytochrome b receives electrons delivered from the primary acceptor complex, and indicate that the photoreduced cytochrome b is reoxidised via an antimycin-sensitive pathway.
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D020130:Bacterial Chromatophores / Q000378:metabolism*; D002844:Chromatium / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D010618:Phenanthrolines / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
chemical_list: D003580:Cytochromes; D010618:Phenanthrolines; D013844:Thiazoles; D000968:Antimycin A