A carboxypeptidase (CP) is an enzyme involved in the catabolism of proteins that cleaves amino acids from the C-terminal of proteins or large peptides through rapid hydrolysis at the last stages of protein cleavage. So far thirteen mammalian CPs encoded by thirteen known members of the metallocarboxypeptidase gene family and one human-specific CP (CPA3) have been identified. Based primarily on amino acid sequence similarities, metallocarboxypeptidases are divided into two subfamilies, including CPA/B family (CPA1, CPA2, CPB, MK-CPA and KPU) and CPN/E family (CPE/H, CPM, CPN, CPD, CPZ, CPX1, CPX2 and AEBP1). All members in CPA/B family are approximately 34-36 kDa proteins of optimal pH=7; while all members in CPN/E family range in size and pH optima.