An algal chloroplast protein possessing latent NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase and latent phosphoribulokinase activities has been purified. Both activities were stimulated by incubation with dithiothreitol and NADPH. The protein had subunit composition 8G6R and on activation depolymerized to discrete NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase (4G) and phosphoribulokinase (2R). Similar depolymerization promoted by reduced thioredoxin could account for light-dependent activations of phosphoribulokinase and NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase observed in algae and higher plants.
