ENERGY-LINKED REACTIONS IN PHOTOSYNTHETIC BACTERIA .3. FURTHER STUDIES ON ENERGY-LINKED NICOTINAMIDE-ADENINE DINUCLEOTIDE REDUCTION BY RHODOSPIRILLUM RUBRUM CHROMATOPHORES

The effect of uncouplers of photophosphorylation on the reduction of oxidized nicotinamideadenine dinucleotide in chromatophore preparations of Rhodosprillum rubrum was that the inhibitory effect of these compounds increased as the light intensity and rate of oxidized nicotinamide-adenine dinucleotide reduction was decreased. Inhibitors of electron transport such as rotenone and 2-heptyl-4-hydroxyquinoline Noxide had the same effect at all light intensities. These results are interpreted to indicate that all of the oxidized nicotinamide-adenine dinucleotide reduction observed in this system is an energy-driven reaction utilizing a high-energy intermediate (I~X) of phosphorylation. The rate of the adenosine triphosphate driven reaction in these chromatophores was generally 15-25% the rate of the light-driven reduction. Several experiments indicated that oxidized nicotinamide-adenine dinucleotide reduction had a greater requirement for I~X than the energy-linked transhydrogenase also found in these preparations. Therefore, the rate-limiting step was postulated to be the formation of I~X. Low concentrations of quinacrine were found to stimulate oxidized nicotinamide- adenine dinucleotide reduction when reduced 2,6-dichloroindophenol was the electron donor but not with succinate or N,N,N′,N′-tetramethyl-p-phenylenediamine as the electron donor. Other studies indicated that quinacrine was stimulating the photooxidation of reduced 2,6-dichloroindophenol. © 1969, American Chemical Society. All rights reserved.