title: Cytochrome b and photosynthetic sulfur bacteria.
abstract: Chromatophores isolated from the purple sulfur bacterium Chromatium and the green sulfur bacterium Chlorobium exhibit absorbance changes in the cytochrome alpha-band region consistent with the presence of a b-type cytochrome. Cytochrome content determined by reduced minus oxidized difference spectra and by heme photochemically active bacteriochlorophyll (reaction-center bacteriochlorophyll). The b-type cytochrome in Chromatium has an alpha-band maximum at 560 nm and a midpoint oxidation-reduction potential of -5 mV at pH 8.0. The b-type cytochrome in Chlorobium has an alpha-band maximum at 564 nm and an apparent midpoint oxidation-reduction potential near -90 mV. Chromatophores isolated from both Chromatium and Chlorobium cells catalyze a photoreduction of cytochrome b that is enhanced in the presence of antimycin A. Antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide inhibit endogenous (but not phenazine methosulfate-mediated) cyclic photophosphorylation in Chromatium chromatophores and non-cyclic electron flow from Na-2S to NADP in Chlorobium chromatophores. These observations suggest that b-type cytochromes may function in electron transport reactions in photosynthetic sulfur bacteria.
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D020130:Bacterial Chromatophores / Q000187:drug effects / Q000378:metabolism*; D002844:Chromatium / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D010084:Oxidation-Reduction; D010087:Oxides / Q000494:pharmacology; D010619:Phenazines / Q000494:pharmacology; D010785:Photophosphorylation / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects; D011199:Potentiometry; D011548:Pseudomonadaceae / Q000378:metabolism*; D011804:Quinolines / Q000494:pharmacology; D013045:Species Specificity; D013053:Spectrophotometry; D013455:Sulfur / Q000378:metabolism
chemical_list: D003580:Cytochromes; D010087:Oxides; D010619:Phenazines; D011804:Quinolines; D000968:Antimycin A; D013455:Sulfur