Genetic heterogeneity of "normal" human erythrocyte glucose-6-phosphate dehydrogenase: an isoelectrophoretic polymorphism.

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Abstract
Quantitative determination of G-6-P dehydrogenase (G6PD; D-G-6-P: NADP+ 1-oxidoreductase, EC 1.1.1.49) activity was carried out in 214 male Nigerian children of 84 mothers with known Gd genotype. The relative intrasibship difference in G6PD activity (normalized to the lowest value within the sibship) was below 0.18 in all cases but one when the children had the same Gd+ allele (identical by descent); whereas it was higher than 0.18 in 18 out of 33 sibships in which children might have had either of the 2 maternal (electrophoretically identical) Gd+ alleles. G6PD from 10 (8 G6PD B and 2 G6PD A) children belonging to 4 of the sibships possessing high quantitative variation in G6PD activity was partially purified and extensively characterized. The 8 G6PD type B samples fell unambiguously into 2 classes on the basis of Km values for glucose 6-phosphate (determined at various pH values), and KCl gradient elution from DEAE-Sephadex columns. The 2 types of G6PD B were resolved from an artificial mixture on a DEAE-Sephacel column. The 2 G6PD type A samples were also different from each other by the same criteria. Normal G6PD is genetically heterogeneous and the structural Gd alleles concerned are all polymorphic in the Nigerian population. In this instance, a human enzyme polymorphism, not associated with enzyme deficiency, was revealed by an approach other than electrophoresis.