On the molecular basis of pyruvate kinase deficiency II. Role of thiol groups in pyruvate kinase from pyruvate kinase-deficient patients

Abstract

1. 1. Human erythrocyte pyruvate kinase (ATP:pyruvate phosphotransferase, EC 2.7.1.40) from the class of pyruvate kinase-deficient patients, characterized by an increased affinity towards phosphoenolpyruvate and a loss of cooperative interaction towards this substrate, shows less affinity for the allosteric inhibitor ATP, when compared to pyruvate kinase from control persons. From the obtained kinetic data we can conclude that the loss of cooperativity towards phosphoenolpyruvate is a consequence of a shift in the R ⇌ T equilibrium to the R state. 2. 2. Incubation of pyruvate kinase, obtained from this class of pyruvate kinase-deficient deficient patients with mercaptoethanol, changes the abnormal kinetics into normal kinetics, as can be conclded from the change in phosphoenolpyruvate dependency and ATP inhibition. 3. 3. The effect of mercaptoethanol on the kinetics of pyruvate kinase from pyruvate kinase-deficient patients suggests that the alteration in the enzyme is a consequence of a modification of the -SH groups. It is suggested that pyruvate kinase deficiency is a secondary defect and that the process which causes the change in the -SH groups of pyruvate kinase, may also be responsible for the increased rate of haemolysis, found in these patients.