Inactivation of Pea Leaf Chloroplastic and Cytoplasmic Glucose 6-Phosphate Dehydrogenases by Light and Dithiothreitol

Abstract

Chloroplastic and cytoplasmic forms of pea (Pisum sativum L.) leaf glucose-6-P dehydrogenase can be separated by gel electrophoresis. Both forms are found in etiolated seedlings. When light-grown plants are illuminated or when crude extracts are treated with dithiothreitol, the chloroplastic and cytoplasmic forms of this enzyme are inactivated. Michaelis-Menten kinetics are obtained for inactivation of the chloroplastic and cytoplasmic glucose-6-P dehydrogenases and for activation of two dehydrogenases involved in photosynthetic carbon metabolism with dithiothreitol. The mechanism for the activation of the two light-activated enzymes appears to be similar to the mechanism for the inactivation of the chloroplastic and cytoplasmic forms of the light-inactivated oxidative pentose phosphate enzyme glucose-6-P dehydrogenase.