Effect of Substrate Structure on the Pre‐Steady‐State Kinetics of Oxidation by Liver Alcohol Dehydrogenase: A Correlation with the Taft σ* Parameter

Abstract

The oxidation of a series of primary alcohols by liver alcohol dehydrogenase has been studied under conditions of [S]0≫ [E]0 using the stopped‐flow method. A biphasic process, with exponential rise to a steady state, was observed for most of the alcohols and the rate constants for the transient phase were determined. No transient phase could be detected for 2‐chloroethanol and 2‐nitroethanol and steady‐state measurements were made for these alcohols. The rate constants for the hydrogen transfer step were obtained from the pre‐steady‐state rate constants for the various alcohols and correlated with the Taft σ* constant. The ϱ* value obtained (−1.8) is consistent with rate‐limiting hydride transfer coupled with removal of the hydroxyl proton by a suitable basic group on the enzyme. A possible identity for this group is suggested. Copyright © 1975, Wiley Blackwell. All rights reserved