APPARENT INHIBITION OF LIVER INSULINASE ACTIVITY BY SERUM AND SERUM FRACTIONS CONTAINING INSULIN-BINDING ANTIBODY

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Abstract
The kinetics of insulinase activity of rat liver homogenate preparations were studied employing insulin-I131. Km for the reaction was 7.9 x 10-8 moles per 1 and Vmax was 18 [mu]g per minute per g liver at 37[degree] C and pH 7.4. Pre-incubation of insulin-I131 with plasma or serum of insulin-treated subjects resulted in inhibition of liver insulinase activity. No such inhibition was observed with serum or plasma of diabetic or nondiabetic subjects who had never been treated with insulin. Inhibition of liver insulinase activity was correlated with the presence of insulin-binding antibody as demonstrated by paper electrophoresis or paper chromatog-raphy. When inhibitory sera were fractionated with cold ethanol, inhibitory activity of the specific fractions was correlated with the presence of insulin-binding antibody. The apparent inhibition of liver insulinase activity by plasma or plasma fractions of insulin-treated subjects is due to the complexing of insulin by insulin-binding antibody.