Evidence for the general base mechanism in carboxypeptidase A-catalyzed reactions: partitioning studies on nucleophiles and H2(18)O kinetic isotope effects.
AUTOR(ES)
Breslow, R
RESUMO
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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=384087Documentos Relacionados
- Heparin-catalyzed inhibitor/protease reactions: kinetic evidence for a common mechanism of action of heparin.
- Kinetic isotope effects in Ras-catalyzed GTP hydrolysis: Evidence for a loose transition state
- Identification and Functional Characterization of Protein Kinase A-catalyzed Phosphorylation of Potassium Channel Kv1.2 at Serine 449*
- Influence of nuclear spin on chemical reactions: Magnetic isotope and magnetic field effects (A Review)
- AB variant of infantile GM2 gangliosidosis: deficiency of a factor necessary for stimulation of hexosaminidase A-catalyzed degradation of ganglioside GM2 and glycolipid GA2.
