Chloroplast and Cytoplasmic Enzymes

Pea (Pisum sativum) leaf chloroplastic and cytoplasmic 3-phosphoglycerate kinases (ATP: d-3-phosphoglycerate 1-phosphotransferase, EC 2.7.2.3) have similar Michaelis constants for ATP, 0.7 and 0.55 mm, for ADP, 0.18 and 0.22, and for 3-P-glycerate, 0.59 and 0.54 mm at low substrate concentrations, and 1.6 and 1.25 mm at high substrate concentrations. Both enzymes are inhibited by ADP and AMP in the ATP-utilizing direction and by ATP and AMP in the ATP-generating direction and are controlled by energy charge. Apparently, whether the cytoplasmic and chloroplastic kinases in the plant cell will participate in the reductive pentose phosphate cycle and gluconeogenesis or in glycolysis will be determined by the environment in the cell compartment and not by the differential properties of the enzymes themselves.