A kinetic study of the inhibition of human and bovine trypsins and chymotrypsins by the inter-alpha-inhibitor from human plasma.

Human plasma inter-alpha-inhibitor forms 1:1 inactive complexes with human and bovine trypsins (EC 3.4.21.4) and chymotrypsins (EC 3.4.21.1). The association and dissociation rate constants as well as the equilibrium dissociation constants (Ki) of the complexes formed of inter-alpha-inhibitor and the four proteases have been measured. The most stable complexes are those formed with the bovine enzymes. For instance, Ki = 2.1-10-11 M for bovine trypsin whereas Ki = 1.2 - 10-8 M for human trypsin. Whatever the species, the complexes formed with the chymotrypsins are less stable than those formed with the trypsins.