Carboxypeptidase peptide link cleavage

Carboxypeptidase A (CPA) is a pancreatic metaUoenz5Tne which catalyses the cleavage of a peptide link in a polypeptide chain. The site of cleavage is specific in two ways it occurs at the C-terminal amino acid (equation 28.22), and it exhibits a high selectivity for substrates in which the C-terminal amino acid contains a large aliphatic or Ph substituent. The latter arises from the presence, near to the active site, of a hydro-phobic pocket in the protein which is compatible with the accommodation of, for example, a Ph group (see below). 

PBPs 4 through 6 are carboxypeptidases responsible for the hydrolysis of i>-alaninc-t>-alanine terminal peptide bonds of the cross-linking peptides. Inhibition of these enzymes is apparently not lethal to the bacterium. even thou cleavage of the terminal t>-alanine bond is requited before peptide cross-linkage. 

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