A new procedure for the purification of proteinase B from baker's yeast and interaction of the purified enzyme with a specific inhibitor.

Proteinase B from baker's yeast was purified to homogeneity by applying affinity chromatography with D,L-tyrosine ethyl ester as ligand. The molecular parameters of the product are similar to those reported formerly by other groups. A different form of proteinase B is isolated if affinity chromatography is replaced by CM-cellulose chromatography and gel filtration. In this case a peptide tightly associated with the enzyme was found to occur. This could be identified as an inhibitor fragment produced by limited proteolysis of a proteinase B bound inhibitor induced by proteinase A.