Interaction of horse plasma antithrombin III and alpha 1-proteinase inhibitor with some serine proteinases.

Antithrombin III and alpha 1-proteinase inhibitor isolated simultaneously from horse citrated plasma were tested for inhibitory activity against bovine trypsin and chymotrypsin, as well as elastase-like neutral proteinases from horse leucocytes. The stoichiometry of reaction and kinetic parameters (kass, Ko) were estimated and related to the protein pattern obtained after exposure of these proteinases to horse inhibitors as analyzed by polyacrylamide gel electrophoresis (PAGE and PAGE-SDS). As shown by fast reaction rates and low values of dissociation constants the two inhibitors effectively inactivate trypsin. On the other hand, AT III is completely inactive against chymotrypsin or leucocyte elastases with alpha 1PI only partly inhibits these enzymes.