Kinetics of the Inhibitory Effect of Pepstatin on the Reaction of Hog Renin with Rat Plasma Substrate

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Abstract
The reaction between hog renin and rat angiotensinogen followed Michaelis-Menten kinetics. A Km value of 1,109 ng angiotensin/ml was determined for the rate of angiotensin formation at pH 7.4 and 37°C. The pH optimum for the reaction of hog renin with rat angiotensinogen was between 6.8 and 7.0. Pepstatin inhibited the reaction in a noncompetitive way. The maximum inhibitory effect occurred at approximately pH 6; at values above pH 8.0, pepstatin had no inhibitory effect. The effect of pepstatin was reversible, since renin activity could be restored by 24 hours of dialysis against distilled water. A 50% inhibition of the enzymatic activity of 0.01 dog units of hog renin was obtained with 0.45 µg pepstatin/ml.