Isolation of chloroplastic phosphoglycerate kinase : kinetics of the two-enzyme phosphoglycerate kinase/glyceraldehyde-3-phosphate dehydrogenase couple

We report here a method for the isolation of high specific activity phosphoglycerate kinase (EC 2.7.2.3) from chloroplasts. The enzyme has been purified over 200-fold from pea (Pisum sativum L.) stromal extracts to apparent homogeneity with 23% recovery. Negative cooperativity is observed with the two enzyme phosphoglycerate kinase/glyceraldehyde-3-P dehydrogenase (EC 1.2.1.13) couple restored from the purified enzymes when NADPH is the reducing pyridine nucleotide, consistent with earlier results obtained with crude chloroplastic extracts (J Macioszek, LE Anderson 1987] Biochim Biophys Acta 892: 185-190). Michaelis Menten kinetics are observed when 3-phosphoglycerate is held constant and phosphoglycerate kinase is varied, which suggests that phosphoglycerate kinase-bound 1,3-bisphosphoglycerate may be the preferred substrate for glyceraldehyde-3-P dehydrogenase in the chloroplast.