MEMORY AND IMPRINTING EFFECTS IN MULTIENZYME COMPLEXES .1. ISOLATION,DISSOCIATION, AND REASSOCIATION OF A PHOSPHORIBULOKINASE-GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE COMPLEX FROM CHLAMYDOMONAS-REINHARDTII CHLOROPLASTS

A bienzyme complex made up of phosphoribulokinase and glyceraldehyde-3 -phosphate dehydrogenase has been isolated and purified from chloropla sts of Chlamydomonas reinhardtii. The complex contains four phosphorib ulokinase and eight glyceraldehyde-3-phosphate dehydrogenase polypepti de chains. As phosphoribulokinase is dimeric and glyceraldehyde-3-phos phate dehydrogenase tetrameric, it is concluded that the complex compr ises two phosphoribulokinase and two glyceraldehyde-3-phosphate dehydr ogenase molecules. Its overall molecular mass is 460 kDa, which is in excellent agreement with its stoichiometry. Moreover, owing to the nat ure of the two enzymes, this complex must catalyse two nonconsecutive reactions. The bienzyme complex tended to spontaneously dissociate int o the free enzymes upon dilution. This dissociation process was consid erably promoted by reducing agents such as dithiothreitol or reduced t hioredoxin. The kinetics of the dissociation process induced by dithio threitol or reduced thioredoxin were paralleled by an increase of acti vity of phosphoribulokinase. The dissociation of the complex was rever sible. If oxidized phosphoribulokinase and glyceraldehyde-3-phosphate dehydrogenase were mixed, a certain amount of the complex was formed. The reconstituted complex displayed properties that were indistinguish able from those of the native complex extracted from chloroplasts of C hlamydomonas reinhardtii. These results suggest that the concentration of the complex in vivo may vary depending on the light intensity.