The cytochrome system of heterotrophically-grown Rhodopseudomonas spheroides

Add time:08/30/2019    Source:sciencedirect.com

Rhodopseudomonas spheroides was grown aerobically in the dark in continuous culture yielding cells with a low bacteriochlorophyll content. The supernatant obtained after cell breakage contained a mixture of cytochromes, apparently of the c-type; these were resolved by spectroscopy at 77°K into three components. The positions of the α, β and γ bands in reduced minus oxidised difference spectra at 77°K were 547, 520 and 417 nm; 549, 520 and 420 nm and 551, 521 and 421 nm, respectively. The 547-nm cytochrome was not readily reduced by ascorbate/tetramethyl-p-phenylene diamine (TMPD) and the 551-nm cytochrome was autoxidisable. Both the 547- and the 549-nm cytochrome were found in the particulate fraction and both were reduced by NADH or succinate in the aerobic steady state and became more oxidised in the presence of antimycin or 2-heptyl-4-hydroxyquinone-N-oxide (HQNO). CO difference spectra of the soluble fraction indicated that it also contained cytochromoid c; maxima were obtained at 569, 539 and 416 nm.The particles were found to contain a mixture of cytochromes. Reduced minus oxidised spectra showed bands at 607 and 445 nm and there was a trough in CO difference spectra at 445 nm indicating the presence of an a type terminal oxidase. Components reacting more slowly with CO yielded maxima at 540 and 570 nm with a trough at 428 nm and sometimes a maximum at 416 nm. These may be due to a mixture of CO-binding pigments in the particles. The α-peak of the b-type cytochromes was asymmetrical in low-temperature difference spectra. Two components were separated spectroscopically; the main component was substrate-reducible and absorbed at 560 nm (557 nm at 77°K); a second component absorbed at 565 nm (562 nm at 77°K) and was found in dithionite-reduced minus substrate-reduced spectra.The small amount of bacterial chlorophyll present in the particles was photo-synthetically active. In the presence of antimycin illumination caused c-oxidation and the reduction of both b-type components.

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