Identification of the binding domain for NADP+ of human glucose-6-phosphate dehydrogenase by sequence analysis of mutants.

Human erythrocyte glucose-6-phosphate dehydrogenase is normally quite stable in the presence of 10 microM NADP+. Certain glucose-6-phosphate dehydrogenase variants lose virtually all their activity at this concentration of NADP+ but are reactivated by 200 microM NADP+. Such variants presumably have a defect in their NADP+-binding site. We analyzed the sequence of cDNA or genomic DNA from seven unrelated patients with hemolytic anemia due to the inheritance of variants that are reactivated by NADP+. Six patients had substitutions of one of three adjacent amino acids, and the seventh patient had another amino acid substitution 23 residues downstream. These amino acids are highly conserved, all being present in rat and all but one being found also in Drosophila. The anomalous electrophoretic behavior of some of the variants can be explained by their loss of ability to bind NADP+. We conclude that the region in which these mutations occur defines the binding domain for NADP+ and that binding NADP+ that has been designated as "structural" and as "catalytic" probably occurs at the same site.