Carboxypeptidase
is Zn containing metalloenzymes that aid protein digestion.
Source:
CP is released in the pancreatic juice of animals. CPC is found in yeast, but it is not a metalloenzyme.
pH effect on CP:
Carboxypeptidase Maximum
(Activity)
i.CPA i. at alkaline pH
ii. CPB ii. at alkaline pH
iii. CPC. iii. at acidic pH
I only discussed here CPA and CPB and as these are well-studied metalloenzymes.
Types of Carboxypeptidase (CP)
CPC is not a Metalloenzyme, it is found in yeast, and it is intracellular. But two others are extracellular.
The requirement to stimulate CPA and CPB:
CPA and CPB need some requirements to stimulate catalytic activity.These are given below:
1. The carboxyl group at C-terminal must be free.
2. Substrates in which the anion acid side chain is aromatic and hydrophobic are favored. But they show somewhat specificity
i) Positively charged side chain is the requirement of CPB.
ii) They do not hydrolyze the proline residue.
3.S configuration of C-terminal residue is necessary.
Structural features of CPA and CPB:
(2,3,8,9,11)
Following are the characteristics structural features of Carboxypeptidase( CP):
Features:
(i) M.wt: about 34,300 Da
(ii) Amino acid residues for CPA-307 and CPB -308.
(iii) Active sites of both are very similar.Structures are
established by X-ray diffraction.
(iv) Metal active site contain Zn(II)
(v) Zinc ligands: His 169, Glu 72, His 196, and H2O (or OH^-)
(vi) Zn(II) is a distorted geometry and coordinated to His 169, Glu 72, His 196, and H2O (or OH^-).
Figure: Structural features of CPA and CPB
Extraction of Zn (II) from CPA and CPB and its consequences: (2)
The laboratory technique used for the removal of Zn (II) from CPA and CPB is dialysis.
The removal is done either at low or neutral pH against a buffer containing a Zinc chelating agent such as Phenanthroline.
Consequences:
Following are the consequences of removals of Zn (II):
The removal of Zn (II) causes:
(i) Loss in the catalytic activity of the enzyme.
(ii) And the little effect on the overall structure.
Role of Zn (II) in CPA and CPB: (2, 3,11)
The amide carbonyl of the substrate molecule replaces the water molecules or (OH^-) and ligates to Zn (II).
The polarized carbonyl group is attacked by an H2O which is activated by Glu-270.
The resulting intermediate is protonated on nitrogen by Tyr-248 and decomposed to amine and carboxylic acid. Thus, a mixed anhydride intermediate is formed and subsequently hydrolyzed.
Conclusion
Investigating many research articles from different well-
known publications and many standard reference books written by many foreign writers and some Indian writers, I have done my article on carboxypeptidase. Sources and teachers encourage me to do this article in a deeper sense.
Reference
The following reference will be used to make this article:
1. Caria scassellati ,Christian Bonvicini ,luisaBenussi, Roberta Ghidoni,Rosanna,Squiti; journal of trace elements in medicine and biology 60,126499,2020
2. Joseph J.Stephanas and Anthony W.Addison; Chemistry of metalloproteins,Wiley series,page-71-87,2014
3. Stephen J.lippard, Jeremy M.Bery; Principles of bioinorganic chemistry ; university science book,page-8,24,259-262;1994
4. Crystal E Valdez, Quentin A Smith, Michael R Nechay, Anastassia N Alexan drove; Accounts of chemical research,47(10),3110-3117,2014; ACS Publication.
5. Tillmann Heinisch, Thomas R Ward; Current opinion in
chemical biology 14(2),184-199,2010, Science direct.com
6. Junghun Suh; Accounts of chemical research 25(7) 273-279, 1992, ACS Publication.
7. Florante A Quiocho, William N Lipscomb; Advances in protein
chemistry 25, 1-78, 1971;
8. M.Benjamin Perryman, JD knell, R Roberts; clinical chemistry 30(5), 662-664, 1984; Oxford Academic.
9. Antonio V.Xavier.VCH; Frontiers in bioinorganic chemistry, 1986.
10. Inorganic Biochemistry, volume- I, 1977, chemicals
society
11. S.P. Banerjee; Advanced inorganic chemistry volume- II,
276-278.
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