Cathepsin S. The cysteine proteinase from bovine lymphoid tissue is distinct from cathepsin L (EC 3.4.22.15).

Cathepsin S was purified from bovine spleen by acid autolysis, (NH4)2SO4 fractionation and chromatography on CM-Sephadex C-50, CM-cellulose and activated-thiol-Sepharose. Cathepsin L was isolated from lysosomal fractions of rat liver, rat kidney and bovine liver. Generally, cathepsin L was bound tightly to CM-Sephadex C-50. Preparations of cathepsin L from rat liver, rat kidney and bovine liver were shown to have kinetic constants for the substrate benzyloxycarbonyl-Phe-Arg-7-(4-methyl)coumarylamide in the same range (Km 2-3 microM). Benzyloxycarbonyl-Phe-Phe-diazomethane proved to be a sensitive irreversible inhibitor of cathepsin L from different species. Cathepsin S differed in all these characteristics from cathepsin L. A polyclonal antibody to cathepsin L from rat reacted with bovine cathepsin L but not with bovine cathepsin S.