SULFIDE-QUINONE AND SULFIDE-CYTOCHROME REDUCTION IN RHODOBACTER-CAPSULATUS

The reduction by sulfide of exogenous ubiquinone is compared to the re duction of cytochromes in chromatophores of Rhodobacter capsulatus. Fr om titrations with sulfide values for V-max of 300 and 10 mu moles red uced/mg bacteriochlorophyll a h,bacteriochlorophyll a.h, and for K, of 5 and 3 mu M were estimated, for decyl-ubiquinone- and cytochrome c-r eduction, respectively. Both reactions are sensitive to KCN, as has be en found for sulfide-quinone reductase (SQR) in Oscillatoria limnetica , which is a flavoprotein. Effects of inhibitors interfering with quin one binding sites suggest that at least part of the electron transport from sulfide in R. capsulatus employs the cytochrome bc(1)-complex vi a the ubiquinone pool.