Carboxypeptidase A3 (mast cell carboxypeptidase A), also known as CPA3, is an enzyme which in humans is encoded by the CPA3 gene. CPA3 has a pH optimum in the neutral to basic range. CPA3 functions together with endopeptidases secreted from mast cells such as chymases and tryptases to degrade proteins and peptides,including the apolipoprotein B component of LDL particles and angiotensin I. Upon mast cell activation and degranulation, CPA3, the chymases, and tryptases are released in complexes with heparin proteoglycan.