Purification and properties of Mucor pusillus acid protease.

The protease produced by Mucor pusillus was recovered from a wheat bran medium by treatment with ammonium sulfate, ethyl alcohol, gel filtration and ion-exchange chromatography. The yield of the enzyme was 55%. The overall increase in the specific activity of the protease was 34-fold. The purified protease was most active at pH 3.8 and 5.6 against hemoglobin and casein, respectively. Optimal hydrolysis of casein was observed at 55 C. The enzyme was stable from pH 3.0 to 6.0. Enzyme inactivated by metal ions was reactivated by ethylenediaminetetraacetate and o-phenanthroline. Reducing agents and thiol poisons had no effect on the protease, suggesting that free sulfhydryl groups were not required for enzyme activity. Diisopropyl fluorophosphate did not inhibit the protease, indicating the probable absence of serine in the active center. The Michaelis-Menten constant for casein was 0.357%. Electrophoretic analysis of active protein recovered by ion-exchange chromatography showed that the protease preparation was homogeneous.