6 carboxypeptidase mechanism

advanced enzymology

1. Carboxypeptidase Mechanism

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

4. 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.

5. •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.

6. •Carboxypeptidase A is a single
polypeptide of 307 amino acid residues.
•There is a tightly bound zinc ion which is
essential for enzymatic activity.

7. •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.

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

9. 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

10. 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.

11. Mechanism