Photophosphorylation in extracts of Rhodospirillum rubrum.

Preparations from a variety of photosynthetic organisms carry out a light-dependent phosphorylation of adenosine diphosphate. These systems appear to be similar in one respect: photophosphorylation is stimulated by substances that may behave as reducing agents, or as electron carriers. In the present study, the photophosphorylation system in extracts of Rhodospirillum rubrum is found to be activated, presumably enzymatically, by such metabolites as succinate, lactate, or reduced diphosphopyridine nucleotide; activity is further increased, but apparently modified, by the addition of phenazine methyl sulfate (1, 2). A similar requirement for carriers such as flavin mononucleotide or menadione has been found by Whatley et al. (3) with spinach chloroplast fragments. A particular characteristic of our system seems to be the almost specific effect of phenazine methyl sulfate, which also has been shown to stimulate photophosphorylation in preparations from Chromatium (4) and spinach (5). The stimulation of spinach preparations by phenazine methyl sulfate recently has been ascribed by Hill and Walker (6) to a photooxidation product of phenazine methyl sulfate, pyocyanine, which, however, does not activate either Chromatium or R. rubrum preparations. One of the major topics in this report will be a detailed description of our experiments on the mode of action of the phenazine dye in the R. rubrum system.