Carboxypeptidases are a class of proteases that cleave peptide bonds at the C-terminal end. They can be further classified by the active site mechanism (eg. metallo-carboxypeptidase, serine carboxypeptidase, cysteine carboxypeptidase) or by substrate preference (carboxypeptidase A, carboxypeptidase B, glutamate carboxypeptidase). Certain carboxypeptidases, such as carboxypeptidase A, are produced as an inactive precursor that becomes activated by cleavage by another protease.