Stoichiometry of Photosynthetic Phosphorylation

The P/2e- ratio of noncyclic photophosphorylation was investigated in the light of recent reports that it is greater than one and may reflect the existence of two types of electron transport, a phosphorylating and a nonphosphorylating type, superimposed on each other. Our results, obtained under experimental conditions that included those reported to be conducive to high ratios, are consistent with the operation in noncyclic photophosphorylation of only one type of electron transport which, in the presence of ADP, orthophosphate, and Mg++, leads to ATP formation with a P/2e- of 1. The reported P/2e- ratios approaching 4 when electron acceptors such as ferricyanide are added at slow rates were not confirmed.