Insulin stimulation of hepatic malic enzyme activity in normal and diabetic rats controlled by different regulatory processes.

A comparison of the processes controlling the increase in hepatic malic enzyme activity in insulin-treated normal and diabetic rats indicated the existence of two distinct regulatory mechanisms. Livers were removed at 12, 36, and 60 h after insulin treatment of normal and alloxan-diabetic rats, and the activity, quantity, and specific activity (units/nmol), of malic enzyme was determined. In normal rats, a significant increase in activity occurred 12 h after insulin, whereas 36 h of insulin treatment was required for diabetic rats to show an increase in enzyme activity. This suggested that the return of malic enzyme activity from the depleted levels measured in diabetic rats probably involved a different sequence of events. A malic enzyme specific radioimmunoassay confirmed this. The increase in activity in insulin-treated normal rats was due to an increase in the quantity of malic enzyme. In insulin-treated diabetic rats, the increase in activity resulted from increases in both enzyme quantity and the specific activity of the enzyme, which returned to levels observed in normal rats.