Glutamine:fructose-6-phosphate amidotransferase activity in cultured human skeletal muscle cells: relationship to glucose disposal rate in control and non-insulin-dependent diabetes mellitus subjects and regulation by glucose and insulin.

We examined the activity of the rate-limiting enzyme for hexosamine biosynthesis, glutamine:fructose-6-phosphate amidotransferase (GFA) in human skeletal muscle cultures (HSMC), from 17 nondiabetic control and 13 subjects with non-insulin-dependent diabetes. GFA activity was assayed from HSMC treated with low (5 mM) or high (20 mM) glucose and low (22 pM) or high (30 microM) concentrations of insulin. In control subjects GFA activity decreased with increasing glucose disposal rate (r = -0.68, P < 0.025). In contrast, a positive correlation existed between GFA and glucose disposal in the diabetics (r = 0.86, P < 0.005). Increased GFA activity was also correlated with body mass index in controls but not diabetics. GFA activity was significantly stimulated by high glucose (22%), high insulin (43%), and their combination (61%). GFA activity and its regulation by glucose and insulin were not significantly different in diabetic HSMC. We conclude that glucose and insulin regulate GFA activity in skeletal muscle. More importantly, our results are consistent with a regulatory role for the hexosamine pathway in human glucose homeostasis. This relationship between hexosamine biosynthesis and the regulation of glucose metabolism is altered in non-insulin-dependent diabetes.