Light- and thiosulfate-dependent reduction of nicotinamide adenine dinucleotides in whole cells of chromatium vinosum

The light-driven, thiosulfate-dependent reduction of nicotinamide adenine dinucleotides under acrobic conditions in whole cells of Chromatium vinosum was investigated.The total concentration of pyridine nucleotides in whole cells was about 50 nmoles per μmole of bacteriochlorophyll. Under dark aerobic conditions, the majority of the nucleotides present was NAD⁺ with about 20% as NADP⁺.About 40% of the total NAD was reduced under continuous illumination. Thiosulfate or sulfide was needed for the photoreduction, while organic acids such as succinate or malate were not. The initial rate of NAD⁺ photoreduction in the presence of thiosulfate was approximately 100 nmoles per μmole of bacteriochlorophyll per min. The NAD⁺ photoreduction was strongly inhibited by uncouplers and electron transfer inhibitors. In contrast, an energy transfer inhibitor, N, N'-dicyclohexylcarbodiimide, did not affect NAD⁺ photoreduction at a concentration at which the light-induced ATP formation was inhibited. A transmembrane electrochemical H⁺ gradient generated by cyclic electron transfer may be the energy source for reduction of NAD⁺ in Chromatium vinosum.