Redox Potentials and Photoreduction by Chloroplast Granules

Abstract

A certain generality exists in the ability of the chlorophyll system to effect the decomposition of water with the help of oxidants and light. Various types of quinones are able to serve as oxidants. The rates of evolution of O2 with the various quinones are, however, a function of their redox potentials. It is found that the rates of O2 liberation by quinones are not equally proportional to the light intensity. With decreasing flux the poorer oxidants become relatively more efficient until at a given low intensity value the rates are actually reversed. At the maximal flux practical saturation has been reached, the rate leveling off more rapidly the poorer the oxidant.