delta pH driven energy-linked NAD+ reduction in Rhodospirillum rubrum chromatophores.

An artificial proton gradient provided sufficient energy to drive reverse electron transport from succinate to NADH:ubiquinone oxidoreductase in chromatophores isolated from Rhodospirillum rubrum. The pH gradient created was able to reduce NAD+. In chromatophores, the optimal rate of NAD+ reduction was about 0.4-0.45 mumol NADH formed/min.mumol bacteriochlorophyll at delta pH 3. The presence of oligomycin was an obligate factor in the assay in order to observe the maximal rate of NAD+ reduction. The rate of NADH formation was dependent on the size of the induced pH gradient. The total NADH formed had a threshold value for the imposed delta pH. The effect of different inhibitors and uncouplers was demonstrated. Comparison between ATP, PPi, and light with the pH jump driven NAD+ reduction rate was studied.