Catalytic and ligand binding properties of bovine trypsinogen and its complex with the effector dipeptide Ile-Val

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Abstract
Steady-state and pre-steady-state kinetic data for the trypsinogen catalyzed hydrolysis of a series of synthetic substrates (i.e. p-nitrophenyl esters of N-α-carbobenzoxy-L-amino acids) have been obtained as a function of pH (3.4–8). Moreover, the effect of ethylamine on the hydrolysis of a neutral substrate and benzamidine binding have been extensively studied. In order to obtain direct information on the transition of trypsinogen to a β-trypsin-like structure, the role of the effector dipeptide Ile-Val on the catalytic and ligand binding properties of the zymogen has been investigated. Kinetic and thermodynamic data for β-trypsin and α-chymotrypsin are also reported for the purpose of an homogeneous comparison of the various (pro)enzymes. In the presence of Ile-Val dipeptide, trypsinogen assumes catalytic and ligand binding properties that are reminiscent of activated β-trypsin. This is at variance with free trypsinogen, which shows a α-chymotrypsin-like behavior. The large differences in the results of kinetic and thermodynamic measurements for free trypsinogen, as compared to its binary adduct with Ile-Val, can be ascribed to the substantial differences in the two molecular species, which include the spatial orientation of Asp189.