Carboxypeptidase B

This chapter describes the activity, specificity and structural chemistry of carboxypeptidase B. Carboxypeptidase B is highly specific for excising C-terminal Lys and Arg residues from peptides and proteins with a preference for arginine. It also acts at a slower rate on C-terminal Val, Leu, He, Asn, Gly or Gin. A preference for Ala in position P2 of synthetic substrates has been observed. Typical assay methods use Bz-Gly-f Arg or FA-Ala┼Arg as substrates. Assays are carried out at pH 7.5–7.8 and 0.1–0.15 M sodium chloride. A number of synthetic inhibitors of basic carboxypeptidases are termed 'biproduct analogs.' Guanidinoethylmercaptosuccinic acid and 2-mercaptomethyl-3-guanidinoethyl-propanoic acid are relevant examples. Other powerful, naturally occurring proteinaceous inhibitors are potato carboxypeptidase inhibitor and leech carboxypeptidase inhibitor, both of which have K values in the nanomolar range. Carboxypeptidase B has been isolated from the pancreas of several species including human , cattle , pig , ostrich and others, and human serum and longitudinal muscle layer of cattle small intestine . A stable enzyme can be purified from pancreatic acetone powder. Internal proteolysis and degradation may occur if the selected source is pancreatic secretion. The purified enzyme is stable for years in the precipitated or the frozen states.