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THE NATURE OF GENERAL BASE-GENERAL ACID CATALYSIS IN SERINE PROTEASES

By L. Polgár and Myron L. Bender

Abstract

The high reactivity of the serine residue at the active site of serine proteases is often attributed to the formation of a hydrogen bond between this serine and a histidine residue. In the case of the serine protease subtilisin, the catalytic serine residue can be specifically replaced by a cysteine residue and this modified enzyme is called thiol-subtilisin. By studying the D2O effect on acyl-enzyme formation with subtilisin and thiol-subtilisin, we present evidence that thiol-subtilisin but not subtilisin may contain a hydrogen bond. Based on the comparison of the catalytic activities of subtilisin and thiol-subtilisin, a rigid active site model for the serine proteases is proposed in which the histidine residue operates in a fixed steric position both as a general base and as a general acid, and this, rather than the formation of a hydrogen bond, accounts for the high nucleophilicity of the serine residue

Topics: Biological Sciences: Biochemistry
Year: 1969
OAI identifier: oai:pubmedcentral.nih.gov:223289
Provided by: PubMed Central
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