Bovine trypsinogen activation. A thermodynamic study.

The N-alpha-L-isoleucyl-L-valine (Ile-Val) activating dipeptide, sequentially homologous to the Ile 16-Val 17 N-terminus of bovine beta-trypsin, displays an activating effect on equilibria involved in the binding of strong ligands (i.e., n-butylamine and the porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, type I; PSTI)) to bovine trypsinogen. This property has been investigated between pH 3.0 and 9.0 (I = 0.1 M) at 21.0 degrees C. The thermodynamics for the interaction of strong ligands with bovine beta-trypsin has also been studied under the same experimental conditions. The equilibria involved in the binding of the Ile-Val activating dipeptide and/or inhibitors to bovine beta-trypsin and its zymogen are described according to linkage relationships, wherefore interaction(s) between different functional and structural domains of the (pro)enzyme (i.e., the so-called Ile-Val pocket and the primary and/or secondary recognition subsite(s)), possibly involved in the bovine trypsinogen-to-beta-trypsin activation pathway, are considered.