Inhibition by Catalase of Dark-mediated Glucose-6-Phosphate Dehydrogenase Activation in Pea Chloroplasts

Dark activation of light-inactivated glucose-6-phosphate dehydrogenase was inhibited by catalase in a broken pea chloroplast system. Partially purified glucose-6-phosphate dehydrogenase from pea leaf chloroplasts can be inactivated in vitro by dithiothreitol and thioredoxin and reactivated by H₂O₂. The in vitro activation by H₂O₂ was not enhanced by horseradish peroxidase, and dark activation in the broken chloroplast system was only slightly inhibited by NaCN. These results indicate that the dark activation of glucose-6-phosphate dehydrogenase may involve oxidation by H₂O₂ of SH groups on the enzyme which were reduced in the light by the light effect mediator system.