Studies on the respiratory system of aerobically (dark) and anaerobically (light) grown Rhodospirillum rubrum.

Abstract

1. A major part of the respiratory activity of light grown cells of Rhodospirillum rubrum is associated with a system identical with that found in dark grown cells. 2. The specific activity of NADH and succinate dehydrogenase and cytochrome c reductase on a protein basis is the same in the particulate fraction from photosynthetic and aerobic cells. In contrast, the NADH and succinate oxidase is more than four times higher in the aerobic cells. Since the amount of particulate protein per cell is almost four-fold less in the aerobic cells, the total particle bound capacity for NADH and succinate oxidation per cell is approximately the same regardless of whether the cells were grown photosynthetically or aerobically. 3. The effect of various inhibitors of NADH oxidation was compared in the particulate fraction from aerobically and anaerobically grown cells. 4,5,6,7-Tetrachloro-2-trifluoromethylbenzimidazole (TTFB) was found to be a potent inhibitor of NADH and succinate oxidation; one-half maximal inhibition was observed at 0.5 μM. Rotenone and amytal inhibited about 80%. 4. In particles from photosynthetically grown cells respiration was inhibited to a maximum of 45–70% by KCN and TTFB; whereas in aerobically grown cells these inhibitors consistently inhibited maximally by more than 70%. 5. NADH oxidation was inhibited 35–50% by light in chromatophore preparations. Antimycin a relieved the light inhibition. In the presence of antimycin a and m-chlorocarbonyl cyanide phenylhydrazone, light stimulated NADH oxidation and the oxidation was not sensitive to KCN. 6. 2-Hydroxy-3-(ω-cyclohexyloctyl)-1,4-naphthoquinone which had little effect on dark NADH oxidation inhibited the light stimulated oxidation. 7. These results indicate that at least three pathways exist for NADH oxidation in chromatophores: a) KCN sensitive which is characteristic of aerobically grown cells; b) KCN insensitive which appears to be part of the cyclic photochemical pathway; and c) the rotenone insensitive pathway.