Phosphoglucose Isomerase from Human Erythrocyte

Phosphoglucose isomerase (D-glucose 6-phosphate ketol isomerase, EC 5.3.1.9) of the human erythrocyte was resolved into a major and two minor components. The major enzyme form, isomerase a, was purified to constant specific activity and appeared homogeneous bjl chromatography, electrophoresis, and ultracentrifugation. The minor enzyme forms, isomerases b and c, were also prepared in high purity in limited quantity. Isomerases a, b, and c differed slightly in their charge properties (isoelectric points at pH 9.2, 9.1, and 9.0, respectively) but were indistinguishable on the basis of molecular size. Sedimentation velocity and partial specific volume measure of isomerase a yielded values of ~~0,~ = 7.0 S and 0.745 cm3 per g. Molecular weight of the native enzyme was 125,000 by sedimentation equilibrium analysis with dissociation induced by denaturing agents yielding two subunits of identical or similar size. Isomerase a was distinguishable from b and c on the basis of a lesser K, for fructose 6-phosphate. Isomerases a, b, and c were identifiable with the major and two minor enzyme forms obtained on electrophoresis of crude hemolysate in starch gel.