Human erythrocyte pyruvate kinase deficiency: The use of a kinetic study of mutant enzymes for the detection of heterozygotes

Erythrocyte pyruvate kinase (PK) deficiency was detected in a boy of dutch origin. Immunologic, electrophoretic, and kinetic studies of the enzymes of propositus and the members of his family demonstrated that the boy was heterozygote for two different mutant PK alleles. The mutant enzyme, for which his mother was heterozygote, was characterized by a lower immunologic specific activity, a decreased affinity for the substrate phospho-enol-pyruvate, and a loss of homotropic interactions toward this substrate, an increased affinity toward the allosteric inhibitor MgATP2-, a decreased affinity for the activator fructose-1,6-diphosphate, and a lowered pH optimum. Electrophoresis, Km app. for MgADP, and the reactivity toward the purine nucleotide substrate analogues were normal. The mutant enzyme for which his father was heterozygote was characterized by a decreased affinity for the substrate phospho-enol-pyruvate and a loss of homotropic interactions toward this substrate. All other parameters mentioned above were normal. The use of a kinetic study of mutant enzymes for the detection of heterozygotes is discussed.