The molecular weight and subunit structure of human erythrocyte 6-phosphogluconate dehydrogenase.

Abstract

6-Phosphogluconate dehydrogenase from human erythrocytes exists predominantly as a species of 104000 molecular weight under various conditions of pH and ionic strength. The s20,w of 5.8 S and D20,w of 51 μm2/s correlate with the molecular weight determined by sedimentation equilibrium. Sedimentation equilibrium experiments indicate a tendency for the enzyme to aggregate on increase in pH or on storage of the enzyme. The aggregates represent an association between six enzyme molecules. 6-Phosphogluconate dehydrogenase was dissociated to subunits of 52000 molecular weight using maleic anhydride or dodecylsulphate-polyacrylamide electrophoresis, indicating that the native enzyme is a dimer. After treatment with maleic anhydride detailed analysis of sedimentation equilibrium data indicates the presence of hexamers in addition to the monomers produced by dissociation. The correspondence between amino-acid composition, subunit size and subunit structure of 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase is discussed.