Formation and Decomposition of Pyrophosphate Related to Bacterial Photophosphorylation

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Abstract
1) When chromatophores from Rhodospirillum rubrum were illuminated with added [32P]P1 and without added ADP, the radioactive P1 was incorporated into some phosphate compounds. A small but definite amount of the compounds thus formed was adsorbed on charcoal, but not the remainder, most of which was purified and identified with pyrophosphate (PP1). 2) The photosynthetic PPi formation required Mg2+ and was stimulated by oligomycin, whereas the photosynthetic ATP formation was stimulated by either Mg2− or Mn2+ and inhibited by the antibiotic. The photosynthetic PP1 formation in the presence of Mg2+ was completely inhibited by Mn2+. 3) Both the photosynthetic PP1 and ATP formations were stimulated and depressed by 2, 6-dichlorophenol indophenol plus ascorbate or phenazine methosulfate, but the optimum concentrations of the redox-reagents were different for these two formations. 4) The photosynthetic PP1 formation was inhibited by ADP, antimycin A, o-phenanthroline, arsenate, and 2, 4-dinitrophenol but not by ATP. The maximum extent of the inhibition by ADP was approximately 40%. 5) Well-washed chromatophores hydrolyzed PP1 into P1. The pyrophosphatase [EC 3.6.1.1] activity was partially depressed in the light even under conditions where the photosynthetic PP1 formation did not occur. The activity in darkness was inhibited by P1 and arsenate, but not by ATP or ADP. It was stimulated by 2, 6-dichlorophenolindophenol, 2, 4-dinitrophenol, Li+, Na+, and K+. 6) When chromatophores were depleted of the quinones, the pyrophosphatase activity in darkness decreased partially. When ubiquinone-10 was added, the activity was restored. 7) By sonication of chromatophores, the pyrophosphatase activity in darkness increased to some extent. 8) The mechanism of the photosynthetic PP1 formation was discussed with relation to that of the photosynthetic ATP formation.

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