Photosynthesis: Primary Physical and Chemical Processes

Abstract

The light-induced absorbancy changes ascribed (at least provisionally) to the oxidation of Ch1 and BCh1, the reduction of PQ and UQ, and the oxidation of Cyt are observed to occur with high quantum efficiencies under unphysiological conditions (e.g., in dry material, and at low temperatures). It can be hoped that these observations constitute an identification of primary photochemical reactants in photosynthesis. Identification of the re-actants, together with an improved understanding of molecular chemistry in condensed systems, should facilitate a more incisive investigation of the primary physical and chemical mechanisms involved in photosynthesis. The "primary" reactions of P700, P890, and Cyt all seem to be of the "one quantum [forward arrow] one electron transfer" type. Their elucidation may be only a partial description of the primary events in photosynthesis, inasmuch as there are still valid arguments in favor of a concerted 2-quantum primary process involving the splitting of H2O. Progressive dehydration has subtle effects on the light-induced absorbancy changes observed in dried bacterial chromatophores. One possible explanation of these effects is that H2O is involved in electron conduction. Another is that H2O is involved directly in the primary photochemical process. There is a bibliography with 115 references.