Regulation of hepatic glucose metabolism by translocation of glucokinase between the nucleus and the cytoplasm in hepatocytes.

We studied the role of glucokinase translocation between the nucleus and the cytoplasm in hepatocytes. In cultured hepatocytes, both the translocation of glucokinase from the nucleus to the cytoplasm and the rate of glucose phosphorylation were increased when cells were incubated with high concentrations of glucose. The addition of low concentrations of fructose, which is known to stimulate glucose phosphorylation, stimulated both glucokinase translocation and glucose phosphorylation. There was a good correlation between the increase in cytoplasmic glucokinase induced by fructose and that in the glucose phosphorylation rate induced by fructose. Furthermore, we observed a linear relationship between cytoplasmic glucokinase activity and rate of glucose phosphorylation over various glucose concentrations in the absence or presence of fructose. These results indicate that glucose phosphorylation in hepatocytes depended on glucokinase in the cytoplasmic compartment--that is, the increase in the rate of glucose phosphorylation was due to the increase in translocation of glucokinase out of the nucleus. Also, oral administration of glucose, fructose, or glucose plus fructose to 24-h fasted rats induced translocation of glucokinase in the liver. All of these results indicate that hepatic glucose metabolism is regulated by the translocation of glucokinase.