Hexose metabolism in pancreatic islets: regulation of mitochondrial hexokinase binding.

A major fraction of hexokinase was found to be bound, presumably to mitochondria, in both normal and tumoral rat pancreatic islet cells examined after either mechanical disruption or digitonin treatment. Spermidine enhanced the binding and glucose 6-phosphate caused the release of hexokinase to and from islet mitochondria, in a manner comparable to that seen in parotid or brain homogenates. In hepatocytes, some hexokinase, but no glucokinase, was found in the bound form. In islet cells, however, the pattern of glucokinase binding was similar to that of hexokinase. It is speculated that the preferential location of both hexokinase and glucokinase on mitochondria may favor the maintenance of a high cytosolic ATP content in islet cells.