EC number3.4.16 - 3.4.18) is an enzyme that hydrolyzes the carboxy-terminal (C-terminal) end of a peptide bond. Humans, animals, and plants contain several types of carboxypeptidases with diverse functions ranging from catabolism to protein maturation.
The first carboxypeptidases studied were those involved in the
digestionof food (pancreatic carboxypeptidases A1, A2, and B). However, most of the known carboxypeptidases are not involved in catabolism; they help to mature proteins or regulate biological processes. For example, the biosynthesis of neuroendocrinepeptides such as insulinrequires a carboxypeptidase. Carboxypeptidases also function in blood clotting, growth factorproduction, wound healing, reproduction, and many other processes.
By active site mechanism
Carboxypeptidases are usually classified into one of several families based on their active site mechanism.
* Enzymes that use a metal in the active site are called "metallo-carboxypeptidases" (EC number 3.4.17).
* Other carboxypeptidases that use active site
serineresidues are called "serine carboxypeptidases" (EC number 3.4.16).
* Those that use an active site
cysteineare called "cysteine carboxypeptidase" (or " thiolcarboxypeptidases")(EC number 3.4.18).
These names do not refer to the selectivity of the amino acid that is cleaved.
By substrate preference
Another classification system for carboxypeptidases refers to their substrate preference.
* In this classification system, carboxypeptidases that have a stronger preference for those amino acids containing
aromaticor branched hydrocarbon chains are called carboxypeptidase A(A for aromatic/ aliphatic).
* Carboxypeptidases that cleave positively charged amino acids (
arginine, lysine) are called carboxypeptidase B(B for basic).
A metallo-carboxypeptidase that cleaves a C-terminal glutamate from the peptide N-acetyl-L-aspartyl-L-glutamate is called "
A serine carboxypeptidase that cleaves the C-terminal residue from peptides containing the sequence -Pro-Xaa (Pro is proline, Xaa is any amino acid on the C-terminus of a peptide) is called "
Some, but not all, carboxypeptidases are initially produced in an inactive form; this precursor form is referred to as a
procarboxypeptidase. In the case of pancreatic carboxypeptidase A, the inactive zymogenform, pro-carboxypeptidase A, is converted to its active form - carboxypeptidase A - by the enzyme enteropeptidase. This mechanism ensures that the cells wherein pro-carboxypeptidase A is produced are not themselves digested.
* Enzyme category
Thrombin-activatable fibrinolysis inhibitoraka plasma "carboxypeptidase" B2
* bacterial transpeptidase, an "alanine carboxypeptidase"
* bradykinin is broken down among other enzymes by "carboxypeptidase N"
* "D-Ala carboxypeptidase" is a
penicillin binding proteins
Phenylalaninemight inhibit "carboxypeptidase A"
* [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=stryer.section.1170 Protease section Stryer book '02]
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