Genetic variants of glucose 6-phosphate dehydrogenase from human erythrocytes: unique properties of the A - variant isolated from "deficient" cells.

The A(-) type of glucose 6-phosphate dehydrogenase (EC 1.1.1.49) has been isolated from human erythrocytes deficient in this enzyme. The specific activity of the purified protein is similar to that previously reported for the enzyme isolated from normal, nondeficient erythrocytes. During the purification procedure, a portion of the A(-) enzyme converts spontaneously, from the native "fraction I", to a "fraction II" having different kinetic and chromatographic properties. The conversion of fraction I to II can be reproduced freely by treatment with iodosobenzoate, and fraction II can be converted back to fraction I by treatment with dithioglycol. We suggest that fraction II is an enzyme species in which one or more sulfhydryl groups have been oxidized to disulfide(s). The tendency to oxidation appears to be a property specific to the A(-) variant and may represent the basis for its rapid rate of inactivation and consequent deficiency in vivo.