Erythrocyte glucose 6-phosphate dehydrogenase of normal and mutant human subjects: properties of the purified enzymes.

A deficiency in human erythrocyte glucose 6-phosphate dehydrogenase may be genetically determined (l-4) or occur in normal erythrocytes as they age in tivo (5, 6). The inherited glucose-6-P dehydrogenase deficiency, which is associated with hemolytic anemia upon exposure to a variety of agents, affords an opportunity in man to study further the mechanisms by which genes can lead to a decrease in the activity of an enzyme. The diminution in enzyme activity with erythrocyte aging in tiuo is relatively selective in that, of the several enzymes studied, only glyceraldehyde 3-phosphate dchydrogenase shows a marked change similar to that of glucose-6-P dehydrogenase (6). This suggests that some specific property of glucose-6-P dehydrogenase may make it peculiarly susceptible to destruction as red cells age. The present investigation has been a study of the properties of glucose-6-P dehydrogenase purified from human erythrocytes. Elucidation of the factors determining the activity and stability of this enzyme is pertinent to the problems of (a) whether in mutant’ subjects, glucose-6-P dehydrogenase deficiency reflects a qualitatively or quantitatively altered protein and, (b) the mechanism of the decrease in enzyme activity as erythrocytes age. Preliminary observations reported by Kirkman (7) and from this laboratory (8) have suggested that the red cell glucose-6-P dehydrogenase of normal and mutant subjects does not differ with regard to the properties of their catalytic site. In the present study, this dehydrogenase has been purified from erythrocytes of normal and Negro mutant subjects. Glucose-6-P, and particularly, triphosphopyridine nuclrotide protect the enzyme against thermal inactivation.* The preparations of enzyme from normal and mutant sources were found to be similar with respect to their stability properties, a wide variety of kinetic parameters, and in their electrophoretic mobility.