Carboxypeptidase D
Carboxypeptidase D (CPD) is a large metallocarboxypeptidase distinguished by a tandem array of three carboxypeptidase-like domains, of which the first two are catalytically active. Unlike secreted digestive carboxypeptidases such as Carboxypeptidase A and B, CPD is a membrane-anchored enzyme that resides primarily in the trans-Golgi network, where it removes C-terminal basic residues from proteins and peptides traversing the secretory pathway and supports maturation of neuropeptide and growth factor precursors. Alternative splicing also yields cytosolic and secreted isoforms. The protein was first identified in duck as a surface glycoprotein bound by duck hepatitis B virus, and its human homolog is broadly expressed, with processing roles that complement the related enzyme Carboxypeptidase E.
