Photosynthetic formation of inorganic pyrophosphate in phototrophic bacteria

In this paper we report studies on photosynthetic formation of inorganic pyrophosphate (PP_i) in three phototrophic bacteria. Formation of PP_i was found in chromatophores from Rhodopseudomonas viridis but not in chromatophores from Rhodopseudomonas blastica and Rhodobacter capsulatus. The maximal rate of PP_i synthesis in Rps. viridis was 0.15 mol PP_i formed/(min*mol Bacteriochlorophyll) at 23°C. The synthesis of PP_i was inhibited by electron transport inhibitors, uncouplers and fluoride, but was insensitive to oligomycin and venturicidin. The steady state rate of PP_i synthesis under continuous illumination was about 15% of the steady-state rate of ATP synthesis. The synthesis of PP_i after short light flashes was also studied. The yield of PP_i after a single 1 ms flash was equivalent to approximately 1 mol PP_i/500 mol Bacteriochlorophyll. In Rps. viridis chromatophores, PP_i was also found to induce a membrane potential, which was sensitive to carbonyl cyanide p-trifluoromethoxyphenylhydrazone and NaF.Abbreviations BChl Bacteriochlorophyll - F₀F₁-ATPase Membrane bound proton translocating ATP synthase - FCCP Carbonyl cyanide p-trifluoromethoxyphenylhydrazone - H⁺-PPase Membrane bound proton translocating PP_i synthase - TPP⁺ Tetraphenyl phosphonium ion - TPB^- Tetraphenyl boron ion - Transmembrane electrical potential difference