Study of the participation of inorganic phosphate as electron donor in primary photosynthetic reactions in Rhodobacter sphaeroides

The formation of ATP during photophosphorylation in chromatophores from purple nonsulfur bacterium Rhodobacter sphaeroides in the presence of phenazine methosulfate and without exogeneous electron carriers under constant illumination and by the action of single light flashes was studied. It was shown that. the photoinduced transport. of electrons to,the exogenous electron acceptor depends on phosphate. It was assumed that phosphate ions are electron donors in the reaction center P870; by the action of light, P870 converts the phosphate ion HPO42- into anion radical HPO4-. In the difference EPR spectra <<light minus darkness>> at 77 K, an asymmetrical doublet signal with a weak low-field line was observed. The signal had a g-tensor of about 2.014 and a hyperfine coupling constant Of about 2.5 mT and belongs probably to the phosphate anion radical.