Kinetics of chymotrypsin- and papain-catalysed synthesis of [leucine]enkephalin and [methionine]enkephalin

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Abstract
The proteinase-catalyzed synthesis of [Leu]enkephalin and [Met]enkephalin was studied kinetically. N.alpha.-t-Butoxycarbonyl-amino acids and peptides or their ethyl esters served as acyl donors, and amino acid phenylhydrazides were used as acyl acceptors. Initial velocity measurements of .alpha.-chymotrypsin-catalyzed peptide synthesis gave rise to kinetic patterns that are compatible with a ping-pong mechanism modified by a hydrolytic branch. Initial rate and alternative substrate inhibition patterns for papain-controlled peptide-bond formation are consistent with a sequential ordered mechanism, with the acyl donor as the obligatory 1st substrate. On the basis of the observed kinetic features, reaction mechanisms are proposed for chymotrypsin- and papain-catalyzed peptide synthesis that inversely equal those describing the pathways of proteolysis. The respective initial velocity expressions for bireactant systems are given, along with the numerical values of the corresponding kinetic parameters.