Regulation of photosynthetic phosphorylation

Abstract

Cyclic, pseudocyclic, and noncyclic photosynthetic phosphorylation are mutually interdependent. Evidence for this is reviewed, in particular where it has to do with regulation of net ATP synthesis during the onset and maintenance of photosynthesis in vivo. It is concluded that both cyclic and noncyclic phosphorylation contribute to photosynthesis and that their relative rates may be controlled by redox poising of their respective electron carriers. The effect of phosphorylation of light‐harvesting‐chlorophyll‐protein on electron transport is to maintain the redox poise of ¡ntersystem electron carriers, notably plastoquinone; it will thereby regulate both cyclic and noncyclic electron transport. The cyclic pathway of ATP synthesis is energetically advantageous only where there exists a mechanism for redistribution of excitation between the photosystems. Protein phosphorylation is therefore implicated in regulation of coupling and stoicheiometry of ATP production and in the maintenance of efficient energy conversion in photosynthesis.