Preparations of ox spleen cathepsin B1 have been found to give multiple peaks of activity upon chromatography on DEAE-cellulose in NaCl gradients or by equilibrium chromatography in 0.05m-NaCl. CM-cellulose gradient chromatography also shows several cathepsin B1 peaks. This evidence indicates that ox spleen cathepsin B1 can exist in at least three to five forms. All forms have the same molecular weight, are thiol-activated and are inhibited by typical thiol inhibitors. The possible sources of this multiplicity of activity are discussed and a possible physiological role for cathepsin B2 is suggested.
