The Effect of Side Chain Structure of Ester Substrates in Determining the Rate-Controlling Step in α-Chymotrypsin-Catalyzed Hydrolysis
- 1 November 1979
- journal article
- research article
- Published by Oxford University Press (OUP) in The Journal of Biochemistry
- Vol. 86 (5) , 1269-1274
- https://doi.org/10.1093/oxfordjournals.jbchem.a132642
Abstract
Presteady state and steady state analyses of the α-chymotrypsin [EC 3.4.21.l]-catalyzed hydrolysis of three specific ester substrates and three ring-substituted derivatives were carried out to elucidate the effect of hydrophobic interactions due to the different side chains of the substrates on the individual steps of the reaction. Hydrolysis of all the substrates except for Nα-acetyl-Nm-formyltryptophan methyl ester (Ac-Trp(CHO)-OMe) was controlled by the deacylation rate. In spite of their comparable K8 values, the substrates with small Kcat, such as .Nα-acetyltryptophan methyl ester and Nα-acetyl-2-(2-nitro-4-carboxyphenyIsulfenyl)-tryptophan methyl ester, characteristically gave Km values one order of magnitude smaller than the others. For the reaction of Ac-Trp(CHO)-OMe, it was ascertained that the deacylation step was not rate-controlling. It is suggested that the acylation step controls the rate in this case.Keywords
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