Aerobic and anaerobic photophosphorylation in spinach-chloroplast preparations under controlled light conditions

Abstract

This report presents an investigation of photophosphorylation in plant-chloroplast preparations under aerobic and anaerobic conditions. The quantum requirement of photophosphorylation at low (rate-limiting) intensities of red light was employed as the assay system. Several catalysts of photophosphorylation, β-naphthoquinone-sulfonic acid, menadione, and phenazine methosulfate showed equal activity under aerobic conditions. The quantum requirement under anaerobic conditions (argon atmosphere) increased (decreased quantum efficiency) with all three catalysts. Anaerobically, photophosphorylation was inhibited by 0.01 N HCN, regardless of catalyst employed. This inhibition was reversed by aerobic conditions. With 0.01 N HCN, O2 uptake and H2O2 production accompanied photophosphorylation under aerobic conditions. With β-naphthoquinone-sulfonic acid or menadione as catalyst the ratio of peroxide production to O2 consumption approached the value 2 as did the ratio of ATP production to O2 consumption. The compounds o-phenanthroline and p-chlorophenyldimethyl urea inhibit photophosphorylation under both aerobic and anaerobic conditions. The inhibition of photophosphorylation is found to be related to the inhibition of Hill-reaction activity brought about by these compounds. Evidence leading to concepts of both cyclic and noncyclic photophosphorylation is discussed. The conclusion is reached that only noncyclic photophosphorylation has been demonstrated in plant-chloroplast preparations.