Hereditary erythrocyte pyruvate kinase deficiency: molecular and functional studies of four mutant PK variants detected in Spain

Abstract

The mechanisms of the defect in enzyme activity and the functional anomalies have been studied for four different mutant erythrocyte pyruvate kinase (PK) variants found in Spain. In two cases the PK variants were heat stable, and their antigenic concentration was nearly normal in the patients' red cells: the defect in activity was due to decreased catalytic activity of the mutant molecules. In the two other observations the mutant PK variants were heat-labile, and their antigenic concentration was reduced in the red cells: the defect in activity was entirely due to this decrease of the enzyme molecule concentration in one case, and to decrease of the enzyme molecule concentration plus decrease of catalytic activity of these mutant molecules in the other case. Kinetic properties were normal for one variant and drastically modified in the three other variants. These latter variants showed decreased apparent affinity for PEP, which cannot be simply explained by a shift of the R α T allosteric equilibrium towards the T form: the results of the study of ATP inhibition and FDP activation, indeed, did not correspond to the expected results for a PK enzyme present in a predominant T form. We point out the heterogeneity and the complexity of the anomalies of the mutant PK variant, most likely reflecting the diversity of the possible punctual mutations of the PK structural gene.