Oxidative Phosphorylation in Extracts of Rhodospirillum rubrum

SUMMARY 1. Cell-free extracts of aerobically grown R. rubrum catalyzed phosphorylation of adenosine diphosphate associated with the oxidation of a variety of substrates in the dark. The P:O ratios varied from below 1 with a variety of citric acid cycle intermediates to a maximum of less than 2 with glucose and related sugar phosphates. 2. The oxidative phosphorylation system consisted of a mix- ture of soluble dehydrogenases and a particulate system. The particles contained reduced diphosphopyridine nucleotide oxi- dase, succinoxidase, and transhydrogenase activities. Soluble components were not required for the phosphorylation carried out by the particles oxidizing DPNH or succinate. 3. The oxidative phosphorylation differed markedly from the anaerobic photophosphorylation catalyzed by extracts of light- grown R. rubrum. The former was not affected by antimycin A, Compound SN5949, and 2-n-nonyl-4-hydroxyquinoline N-oxide, whereas the latter was strongly inhibited. Further- more, Amytal, which inhibited DPNH oxidation and associated phosphorylation, did not appreciably affect photophosphoryla- tion. Finally, phenazine methosulfate, which stimulated photo- phosphorylation, inhibited oxidative phosphorylation. 4. Oxidative phosphorylation was carried out by extracts of light-grown R. rubrum and appeared to be associated with the “chromatophore” system which catalyzed photophosphoryla- tion. The oxidative phosphorylation of anaerobically light- grown and aerobically dark-grown R. rubrum were affected in the same manner by inhibitors. 5. An analysis of extracts indicated that preparations from dark-grown and light-grown R. rubrum contained approximately the same amounts of cytochromes b and ~2; on the other hand, the latter extracts contained more than 10 times as much co- enzyme Q and Rhodospirillum heme protein as the former. Acknowledgments-The author is deeply indebted to Dr. Howard Gest for helpful advice during this investigation and for penetrating criticism during the preparation of this report. He also wishes to acknowledge the assistance of Dr. Bernard Shore in the ultracentrifuge analyses. REFERENCES 1. FRENEEL, A.,