Species variants of cathepsin L and their immunological identification.

Cathepsin L variants purified from sheep and ox liver are shown to have similar catalytic properties to those from rat, rabbit and man with regard to activity against the substrate benzyloxycarbonyl-Phe-Arg-7-(4-methyl)coumarylamide and inhibition by benzyloxycarbonyl-Phe-Phe-diazomethane, thus identifying cathepsin L in these species for the first time. All five variants of cathepsin L are shown to be immunologically related by their interaction with antibodies raised to the human enzyme. Sheep liver was found to yield more enzyme than any other species, suggesting that this tissue is a good source of cathepsin L. Cathepsin S, a closely related enzyme, could not be detected in livers of any of these species.