– Carboxypeptidase A4 (CPA4) is a member of the peptidase M14 family. CPA4 is metalloprotease that could be involved in the histone hyperacetylation pathway. CPA4 binds one zinc ion per subunit and could catalyze to release of a C-terminal amino acid, with preference for -Phe, -Leu, -Ile, -Met, -Tyr and -Val.They have distinct expression patterns and different specificities for example, preferentially cleaving aromatic (carboxypeptidase As) or basic (carboxypeptidase Bs) residues. Several, such as carboxypeptidase Xs, have lost their catalytic activity. Carboxypeptidases play important roles in digestion of food, processing of bioactive peptides and blood coagulation.