Isolation and characterization of cathepsin B from rabbit testis

Cathepsin B (EC 3.4.22.1) has been purified from rabbit testes to apparent homogeneity by chromatography on DE-52, affinity chromatography on organomercurial agarose and subsequent gel filtrations on Sephadex G-75. The enzyme is composed of a single polypeptide of Mr 23,000. Thiol blocking agents and leupeptin abolished the activity of the enzyme completely. The enzyme showed maximum activity at pH 6.0 and 43 degrees C, required 2 mM-cysteine for the optimal activity and had a Km1.45 X 10(-3) M using Z-Arg-beta-naphthylamide as the substrate. However, Z-Arg-Arg-beta-naphthylamide was 12 times more sensitive as a substrate than was Z-Arg-beta-naphthylamide. Rabbit testicular cathepsin B hydrolysed intact proteins. An endogenous inhibitor isolated from the rabbit testes inhibited purified Cathepsin B.