Substrate activation of rat trypsins 1 and 2

Qualitative differences in the active center of rat trypsins 1 and 2 resulted in different ratios of K_cat for N¹-tosyl-l-arginine methyl ester vs K_cat for N¹-benzoyl-l-arginine ethyl ester. These ratios were 2.5 for trypsin 1 and 1.2 for trypsin 2.Substrate activation with N¹-tosyl-l-arginine methyl ester enhanced the catalytic rate constant of rat trypsin 1 2.5-fold and that of rat trypsin 2 only 1.5-fold. The increase in the catalytic rate constant found with N¹-benzoyl-l-arginine ethyl ester was the same (1.5-fold) for both trypsins. Consequently, at 20 mm substrate concentration, trypsin 1 catalyzed the esterolysis of N¹-tosyl-l-arginine methyl ester 4.5 times faster than that of N¹-benzoyl-l-arginine ethyl ester, while trypsin 2 was only 1.3 times more efficient with the first substrate.Furthermore, the activation of both rat enzymes by N-acetyl-l-tyrosine ethyl ester was even more effective than that obtained with the two cationic esters; the maximum rates of hydrolysis of this neutral substrate by trypsins 1 and 2 were enhanced 120- and 50-fold, respectively, by high concentrations of N-acetyl-l-tyrosine ethyl ester.