[Cathepsin D from horse spleen. II. Study of certain enzymatic properties]

This work reports some enzymatic properties of highly purified horse spleen cathepsin D. Hydrolysis rate of several proteins are compared. The Kinetic constants (Km = 4.95 10(-5) M and Vm = 1,76 delta DO/mn/mug) have been determined in the presence of a denatured haemoglobin substrate. Stability of the enzymatic preparation is discussed according to the pH, concentration and time of storage. Some investigations concerning the active site are described. Enzymatic and chemical results show that dicarboxylic and tryptophanyl residues seem to be involved in the hydrolytic process. Catalysis does not depend on sulfhydryl or seryl residues. Different salts, particularly nitrate, nitrite and polyphosphate are potent inhibitors of enzymatic activity.