Nonenzymatic Glycosylation of Erythrocytic Proteins in Normal and Diabetic Subjects: Enzymes of Nucleoside and Nucleotide Metabolism

Abstract

A modification of the technique of Glyco-Gel affinity column chromatography has been employed to separate glycosylated proteins from nonglycosylated proteins of hemolysates. When glycosylation in hemolysates of 11 type I diabetic subjects was compared with that from 7 normal subjects, significant increases were found in glycosylation of hemoglobin (Hb) (12.1 ± 6.0% versus 4.7 ± 0.5%) and purine nucleoside phosphorylase (PNP) (5.3 ± 3.0% versus 2.1 ± 0.5%). However, no differences were found for nucleoside diphosphokinase (NDPK) (1.5 ± 1.1% versus 1.0 ± 0.4%) and adenylate kinase (AMPK) (0.5 ± 0.4% versus 0.7 ± 0.2%). Linear relationships were seen between glycosylated Hb and glycosylated PNP (r = 0.97) or glycosylated NDPK (r = 0.81). On incubation of hemolysates from normal individuals with high glucose (1500 mg/dl or 83 mM) and NaCNBH3 (20 mM), linear increases in the degrees of glycosylation were seen with time. After 18 h, the percentages of glycosylation of Hb, PNP, NDPK, and AMPK were increased from normal values to 31, 24, 11, and 3, respectively. When partially purified human erythrocytic PNP was incubated with various monosaccharides (20 mM) in the presence of NaCNBH3 for 6 h, glycosylation increases of 2–5-fold were seen in the order ribose > mannose > galactose > glucose.