Possible initial events of photophosphorylation in membranes of Rhodopseudomonas viridis and Rhodopseudomonas capsulata Ala+r

Photosynthetic formation of inorganic pyrophosphate in phototrophic bacteria

In this paper we report studies on photosynthetic formation of inorganic pyrophosphate (PPi) in three phototrophic bacteria. Formation of PPi was found in chromatophores from Rhodopseudomonas viridis but not in chromatophores from Rhodopseudomonas blastica and Rhodobacter capsulatus. The maximal rate of PPi synthesis in Rps. viridis was 0.15 μmol PPi formed/(min*μmol Bacteriochlorophyll) at 23°C. The synthesis of PPi was inhibited by electron transport inhibitors, uncouplers and fluoride, but was insensitive to oligomycin and venturicidin. The steady state rate of PPi synthesis under continuous illumination was about 15% of the steady-state rate of ATP synthesis. The synthesis of PPi after short light flashes was also studied. The yield of PPi after a single 1 ms flash was equivalent to approximately 1 μmol PPi/500 μmol Bacteriochlorophyll. In Rps. viridis chromatophores, PPi was also found to induce a membrane potential, which was sensitive to carbonyl cyanide p-trifluoromethoxyphenylhydrazone and NaF.

Initial events of light-dependent ATP synthesis in spinach subchloroplast particles

The kinetics of 32Pi incorporation into adenine nucleotides by subchloroplast particles in the light is studied with a continuous flow apparatus allowing measurements between 3 and 200 ms. After a short lag time from 1 to 3 ms ATP synthesis proceeds with a constant rate. During the first few milliseconds a faster labelling of ADP is detected. This labelling of ADP reaches a constant level up to 1 molecule ADP labelled per molecule of coupling factor present. The labelling pattern in ATP indicates that the labelled ADP does not equilibrate with free ADP. The addition of 32Pi to a phosphorylating system during the light phase (32Pi pulse) exhibits unchanged kinetic characteristics for labelling of ATP and ADP. These results indicate a phosphorylation of AMP to ADP being an intermediate step in photophosphorylation. In experiments carried out in the dark no label is found in ATP within the time analysed. However the labelling of ADP occurs in the same way as in the light.