Light-induced cytochrome c redox reactions by a cell-free preparation of Anabaena cylindrica

Abstract

The Anabaena preparation always oxidized cytochrome c in the light under both aerobic and anaerobic conditions if the added cytochrome c was even partially reduced. Light oxidation was always followed by a reduction in the following dark period. Amounts of cytochrome c reduced in the dark were far larger under anaerobic conditions ( 1 10 of chlorophyll a content in the reaction mixture) than under aerobic conditions ( 1 30 of chlorophyll a content). 3-(2,4-dichlorophenyl)-1,1′-dimethyl urea) inhibited the dark reduction only under aerobic conditions and with partially reduced cytochrome c. Benzyl viologen, flavine mononucleotide, and diquat suppressed the aerobic dark reduction but strongly stimulated the aerobic light oxidation. Anaerobic redox reaction was not affected by benzyl viologen. Phenazine methosulfate inhibited both aerobic and anaerobic redox reactions. Results were taken as evidence for the previously proposed hypothesis that the Anabaena preparation contains a large amount of a redox substance(s), tentatively named cytochrome c reducing substance (CRS), which mediates electron transfer from system 1 to oxidized cytochrome c.