CPO (Carboxypeptidase O) is a member of the M14 family of metallocarboxypeptidases, belonging to the CPA subfamily. It is a GPI-anchored membrane-bound enzyme highly expressed on the brush-border membrane of intestinal epithelial cells. Unlike classical digestive carboxypeptidases such as CPA and CPB, which are secreted as inactive proenzymes, CPO is synthesized as an active enzyme without a prodomain. Its most distinctive biochemical feature is a strong substrate preference for C-terminal acidic amino acids, specifically glutamate and aspartate. This specificity distinguishes CPO from other family members. Its primary physiological role is to complete the digestion of dietary proteins by releasing acidic amino acids for efficient absorption in the small intestine.