CPA4, also known as carboxypeptidase A4, is a secreted, zinc-dependent metallocarboxypeptidase that removes the C-terminal amino acid from peptides having a free C-terminal carboxyl group. CPA4 is synthesized as zymogens that are activated by proteolytic cleavage. Recombinant human CPA4, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.