Glucokinase is concentrated in insulin-secretory granules of pancreatic B-cells.

We immunohistochemically examined the distribution of glucokinase (GK) in the B-cells of pancreatic islets of normal rats. GK was stained punctately in the cytoplasm of B-cells when examined under the light microscope. By use of a double-immunostaining technique, most of the GK immunoreactivity was observed to be colocalized with insulin immunoreactivity. Electron microscopic examination by the immunogold method revealed that GK immunoreactivity was predominantly located within insulin-secretory granules of pancreatic B-cells. Exploration of the intracellular distribution of GK in hepatocytes suggested that the shuttling of the enzyme between the nucleus and the cytoplasm is essential for the regulation of GK activity (Toyoda et al. 1994, 1995, 1996a,b, 1997a). As an approach to the elucidation of the mechanism of control of GK activity, we immunohistochemically investigated the intracellular distribution of the enzyme in pancreatic B-cells under both light microscopy and electron microscopy in this study. A preliminary report of the present study has been published.