P-2e-ratios approaching 4 in isolated chloroplasts.

Previous studies of Arnon, Whatley, and Allen (I), Krogmann, Jagendorf, and Arnon (Z), Good (3), and Stiller and Vennesland (4) have indicated that in noncyclic photophosphorylation only 1 adenosine triphosphate molecule is produced per pair of electrons. However, Winget, Isawa, and Good (5) have recently observed P/2eratios of 1.3 with the use of chloroplasts from various species incubated at a high pH (pH 8.5). Also, Nishimura (6), from studies on delayed photophosphorylation in Rhodospirillum rubrum chromatophores, has calculated that the P/2evalue may be as high as 4. The studies of Baltscheffsky and Arwidsson (7), as well as those of Gorman and Levine (8), on mutants of Chlamydomonas reinhardi which have lost either cytochrome f or plastocyanin, also suggest hat more than one site for phosphorylation exists along the linear electron chain of chromatophores and chloroplasts. Current investigations in this laboratory have shown that the P/2eratio for noncyclic photophosphorylation in isolated fresh market spinach (Spinacia oleracea) chloroplasts approaches 4, by the use of either benzoquinone or ferricyanide as the electron acceptor. These high P/2eratios were not observed when nicotinamide adenine dinucleotide phosphate in the presence of added spinach ferredoxin was the terminal electron acceptor, although a ratio of slightly over 1 (1.3) was observed.