Rat islets contain the acid-labile activator of phosphofructokinase, fructose-2,6-bisphosphate. The islet content in activator is higher in islets exposed to glucose (16.7 mM) than in islets deprived of glucose. The islets display fructose-6-phosphate, 2-kinase activity with a Km for fructose-6-phosphate close to 0.08 mM. Glucose fails to affect the activity of this enzyme. It is proposed that the effect of glucose to increase the islet content of fructose-2,6-bisphosphate is attributable, in part at least, to the glucose-induced increase in the concentration of fructose-6-phosphate in the islet cells.

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