Mechanism of action of carboxypeptidase A in ester hydrolysis.
AUTOR(ES)
Makinen, M W
RESUMO
The reaction of carboxypeptidase A (peptidyl-L-amino-acid hydrolase; EC 3.4.12.2) with the specific ester substrate O-(trans-p-chlorocinnamoyl)-L-beta-phenyllactate has been investigated in the temperature range 25 degrees to -40 degrees with use of organic-aqueous cosolvent mixtures. In the subzero temperature range the hydrolysis reaction is characterized by a biphasic decrease in absorbance specific for the substrate. The kinetic data can be unambigously analyzed as two consecutive first-order reactions with formation of a covalent acyl-enzyme intermediate. Deacylation of the covalent intermediate is shown to be rate-limiting in the subzero temperature range, and near -60 degrees it is sufficiently stable for spectral characterization. Consideration of the structure of the active site and of the catalytically functional residues of the enzyme leads to the conclusion that the intermediate is a mixed anhydride in which the gamma-carboxylate of glutamate-270 is acylated by the substrate. The temperature dependence of the rate constants of the acylation and deacylation steps explains why the intermediate of this enzyme-catalyzed reaction is observed only at low temperatures.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=431251Documentos Relacionados
- A Mechanism of Action for Carboxypeptidase A
- Mechanism of chaperonin action: GroES binding and release can drive GroEL-mediated protein folding in the absence of ATP hydrolysis.
- The Role of a Tyrosyl Residue in the Mechanism of Action of Carboxypeptidase B: Luminescence Studies
- Rapid test for determination of esculin hydrolysis.
- X-ray crystal structures of transforming p21 ras mutants suggest a transition-state stabilization mechanism for GTP hydrolysis.