Activation and inhibition of human erythrocyte pyruvate kinase by organic phosphates, amino acids, dipeptides and anions

Abstract

1. 1.|Human erythrocyte pyruvate kinase (ATP:pyruvate phosphotransferase, EC 2.7.1.40) has been proposed to conform to the two state conformational model for allosteric enzymes of Monod, Wyman and Changeux. We have examined the kinetic properties of the enzyme in this light and where appropriate made comparative studies on the non-allosteric isozyme from rabbit muscle. 2. 2.|In the pH range from 7 to 8 at low phosphoenolpyruvate concentration the erythrocyte enzyme activity has a strong pH dependence. This behaviour is of practical concern in the conditions used for blood banking. 3. 3.|A number of intracellular organic phosphates were tested. The most likely physiological activators of the erythrocyte enzyme are glucose 6-phosphate and fructose 1,6-diphosphate. Conflicting reports on the effect of 2,3-diphosphoglycerate on the enzyme appear due to differences in the magnesium concentration used in the assays. 4. 4.| l-Amino acids inhibit human erythrocyte pyruvic kinase in a pH and substrate-concentration dependent manner. Various alanine depeptides activate the erythrocyte enzyme, others inhibit. Dipeptides give only inhibition with the muscle enzyme. 5. 5.|Anions inhibit both enzymes. Inhibition of the erythrocyte enzyme is pH and substrate-concentration dependent. 6. 6.|All of these observations are consistent with alterations in the R ⇌ T equilibrium proposed for human erythrocyte pyruvate kinase.