Interactions of catalytic cofactors for photosynthetic phosphorylation with Hill reaction oxidants.

Oxidation-reduction reactions in chloroplasts were first 01 served when Hill (1) discovered photolysis by isolated chloro plasts. In the Hill reaction electron transport proceeds from water to the artificial oxidant which can be any one of a number of compounds (24). A cyclic series of oxidation-reduction reactions is postulated as the basis for photosynthetic phosphorylation by spinach chloroplasts (5). In phosphorylation water is presumably cleaved and then regenerated. In order for the regeneration of mater to occur an oxidation-reduction cofactor must be added in catalytic amounts, and again a large variety of compounds will function (‘53. Our primary question is whcthcr the Hill reaction and cyclic phosphorylation share all or most of the same electron transport pathways in chloroplasts, or whether there is a different set of intermediate carriers for the two over-all reactions. The similar action spectra for the two reactions (8, 9) and the existence of phosphorylation during the Hill reaction (10) argue for a basic similarity. Further evidence is obta,ined from experiments with misturcs of Hill oxidants and catalytic cofactors, to be reported in this paper.