Utility of 3-O-methyl-N-acetyl-D-glucosamine, an N-acetylglucosamine kinase inhibitor, for accurate assay of glucokinase in pancreatic islets and liver.

Glucokinase, an enzyme that catalyzes the phosphorylation of glucose, constitutes the key regulatory step in glucose metabolism in pancreatic islets and liver. We found that 3-O-methyl-N-acetyl-D-glucosamine (3-O-methyl-GlcNAc) potently inhibits glucose phosphorylation by N-acetylglucosamine kinase whereas glucokinase is not at all affected by this hexosamine. The addition of 3-O-methyl-GlcNAc to the assay system for glucokinase in rat liver extracts, which contain a high activity of glucokinase (glucose as substrate) relative to N-acetylglucosamine kinase (N-acetyl-D-glucosamine as substrate), affected neither Km nor Vmax values of glucokinase. On the other hand, both Km and Vmax values of glucokinase in rat pancreatic islet extracts, in which N-acetylglucosamine kinase activity is higher than glucokinase activity, were significantly lowered by the use of 3-O-methyl-GlcNAc as an inhibitor of N-acetylglucosamine kinase.