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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1983 Jul;80(14):4585–4589. doi: 10.1073/pnas.80.14.4585

Evidence for the general base mechanism in carboxypeptidase A-catalyzed reactions: partitioning studies on nucleophiles and H2(18)O kinetic isotope effects.

R Breslow, J Chin, D Hilvert, G Trainor
PMCID: PMC384087  PMID: 6576353

Abstract

Methanol does not detectably compete with water in carboxypeptidase-catalyzed cleavage of any substrate, although it is preferentially reactive in a model for the proposed nucleophilic mechanism for the enzyme that involves an anhydride intermediate. To test for such a common intermediate in the cleavage of related peptide and ester substrates, a method has been developed to examine H2(16)O-H2(18)O kinetic isotope-partitioning effects. The finding that benzoylglycylphenylalanine has an isotope effect of 1.019 +/- 0.002 while benzoylglycyl-beta-L-phenyl-lactate shows a small inverse isotope effect excludes most versions of a nucleophilic mechanism having a common anhydride intermediate. The bulk of the available evidence strongly favors the previously proposed general base mechanism.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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