Carboxypeptidase Mechanism

• Carboxypeptidase A is a digestive enzyme that hydrlyzes the carboxyterminal peptide bond in polypeptide chain.

Two aspects of catalytic mechanism will be discussed for carboxypeptidase A:

• Induced Fit: The binding of

substrate is accompanied by quite large alteration in the structure of the active site.

• Electronic strain:

The enzyme contains Zinc atom and other groups at the active site that induce electronic rearrangement of the substrate to be more susceptible to hydrolysis.

• Carboxypeptidase A is a single polypeptide of 307 amino acid residues.

• There is a tightly bound zinc ion which is essential for enzymatic activity.

• Zinc is located in a groove near the surface of the molecule ccordinated in a tetrahedral array of two histidine side chain, a glutamate side chain and a water molecule.

• The Carboxyl oxygen of the peptide bond to be cleaved is ccordinated with the zinc ion

1-The tyrosine side chain of the substrate binds to the non-polar pocket in the active site of the enzyme.

2-The NH- hydrogen of the peptide bond to be cleaved is hydrogen bonded to the OH group of tyrosine 248.

3-The negatively charged terminal carboxylic group of glycyltyrosine (substrate) interacts electrostatically with the positively charged side chain of arginine 145

4-The carboxyl oxygen of the peptide bond to be cleaved is coordinated to the zinc ion.

5-The terminal amino group of the peptide chain is hydrogen bonded through the water molecule to the side chain of glutamate 270.

Mechanism