[Biochemical study on nonenzymatic glycosylation of human erythrocyte Cu-Zn-superoxide dismutase].

Human erythrocytes contain glycosylated and nonglycosylated Cu-Zn-superoxide dismutases which can be separated by boronate affinity chromatography. The percentage of the glycosylated form is significantly increased in the erythrocytes of the patients with diabetes as compared to normal erythrocytes. The nonglycosylated Cu-Zn-superoxide dismutase, which was washed through the boronate column, was glycosylated in vitro upon exposure to radioactive or nonradioactive D-glucose. Incorporation of D-glucose into the protein was observed, and with increase in glycosylation, the enzymatic activity decreased, indicating that the glycosylation of the enzyme led to low active form. The sites of glycosylation of the superoxide dismutase were identified by amino acid analysis after reverse-phase high performance liquid chromatography of the trypsin-treated peptides.