Isolation and characterization of two protease inhibitors from bovine plasma

Two protease inhibitors (Inh2 and Inh3) from bovine plasma have been isolated and characterized. The apparent molecular weights of the two proteins are 56 and 58 kDa, respectively. Although Inh2 and Inh3 both inhibit trypsin and human neutrophil elastase, only Inh3 is a good inhibitor of chymotrypsin and cathepsin G. Inh3 is much more sensitive to oxidation than Inh2. One murine monoclonal antibody recognizes Inh3 but not Inh2. Inh3 resembles human alpha 1-antitrypsin both structurally and functionally. Inh2, on the other hand, has some structural homology to human alpha 1-antichymotrypsin, but its specificity does not correspond to that of either human alpha 1-antitrypsin or human alpha 1-antichymotrypsin.