Feb 7, 2001

Inhibition Effects in the Hydrolysis Reactions of Esters and Peptides Catalyzed by Carboxypeptidase A: An Example of Cooperative Binding Effects with a Monomeric Enzyme

Bioorganic Chemistry
A Rahmo, T H Fife

Abstract

N-benzoyl-L-phenylalanyl-L-phenylalanine is an excellent peptide substrate for carboxy-peptidase A; at 30 degrees C and pH 7.5, K(m) is 2.6 x 10(-5) M while k(cat) is 177 s(-1) (k(cat)/K(m) = 6.8 x 10(6) M(-1) s(-1)). Indole-3-acetic acid is a noncompetitive or mixed inhibitor towards the peptide and toward hippuryl-L-phenylalanine; plots of E/V vs [Inhibitor] are linear. N-Benzoyl-L-phenylalanine is a competitive inhibitor of peptide hydrolysis, and plots of E/V vs [Inhibitor] are again linear. One molecule of inhibitor binds per active site, and these inhibitors bind in different sites. At constant peptide substrate concentration and a series of constant concentrations of indole-3-acetic acid, plots of E/V vs the concentration of N-benzoyl-L-phenylalanine are linear and intersect behind the E/V axis and above the [Inhibitor] axis. This shows that both inhibitors can bind simultaneously and that binding of one facilitates the binding of the other (beta = 0.18). Employing the ester substrate hippuryl-DL,beta-phenyllactate, the same type of behavior is observed in the reverse sense; N-benzoyl-L-phenylalanine is a linear noncompetitive inhibitor and indole-3-acetic acid is a linear competitive inhibitor. Again the two inhibitor p...Continue Reading

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Mentioned in this Paper

Pentosuria
Plain X-ray
Aminopeptidase
CNDP2 gene
TACSTD2
Penicillopepsin
Binding (Molecular Function)
Indoleacetic acid
Radiographic Imaging Procedure
Esters

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