Light-induced electron transfer, internal and external hydrogen ion changes, and phosphorylation in chromatophores of Rhodospirillum rubrum

Abstract

Light-induced electron transfer, internal and external hydrogen ion changes (measured by bromthymol blue and glass electrode methods), and phosphorylation in the isolated chromatophores of Rhodospirillum rubrum were studied under phosphorylating and nonphosphorylating conditions. Under nonphosphorylating conditions, hydrogen ion changes saturated at a lower intensity of excitation light than under phosphorylating conditions. The maximum amounts of nonphosphorylating hydrogen ion changes (internal and external) were much smaller than those of phosphorylating changes. Utilization of the high-energy compound or high-energy state by phosphorylation of ADP competed with the utilization of energy by the process which induces internal acidification. The absence of ADP or addition of oligomycin increased the light-induced internal acidification. The process of internal acidification was slower than phosphorylation. Therefore, it cannot precede phosphorylation. Branching of phosphorylation and internal acidification in the energy transduction chain occurs at the stage of high-energy intermediate. The kinetics of the light-induced absorbance change was markedly affected by phosphorylation. Effects of electron-transfer inhibitors, an accelerator, and uncouplers of phosphorylation on the absorbance changes and internal and external hydrogen ion changes were studied. Electron transfer was a prerequisite for the hydrogen ion changes. The processes of hydrogen ion changes and phosphorylation were most closely connected with the dark electron transfer in the time range of 10 −3-10 −2 second after pulse excitation. On the other hand, no effect of different phosphorylating conditions or reagents was observed in the rapid light-induced phase of electron transfer.