Carboxypeptidase A2 (CPA) is a secreted pancreatic procarboxy-peptidase that cleaves the C-terminal amide or ester bond of peptides that have a free C-terminal carboxyl group. The hydrolytic action of CPA2 was identified with a preference towards long substrates with aromatic amino acids in their C-terminal end, particularly tryptophan. CPA2 comprises a signal peptide, a pro region and a mature chain, and can be activated after cleavage of the pro peptide. Three different forms of human pancreatic procarboxypeptidase A have been isolated, and the A1 and A2 forms are always secreted as monomeric proteins with different biochemical properties. In contrast to procarboxypeptidase B which was always secreted by the pancreas as a monomer, procarboxypeptidase A occurs as a monomer and/or associated to one or two functionally different proteins, such as zymogen E, and is involved in zymogen inhibition.
Carboxypeptidase B1 is an exopeptidase which specifically cleaves the C-terminal Arg and Lys residues with a preference for Arg. Expressed mainly in pancreas, CPB1 is a useful serum marker for acute pancreatitis and pancreatic graft rejection.Human CPB1 consists of a signal peptide, a pro region, and a mature chain. The purified rhCPB1 corresponds to the pro form, which can be activated by trypsin, the only pancreatic protease capable of generating active enzyme from the zymogen in vitro.
Carboxypeptidase B1, also well known as pancreatic procarboxypeptidase B (PCPB), is a highly pancreas -specific protein (PASP), and has been identified previously as a serum marker for acute pancreatitis and pancreatic graft rejection. As the prototype for those human exopeptidases that cleave off basic C-terminal residues, CPB1 specifically cleaves the C-terminal Arg and Lys residues with a preference for Arg. The B1 and B2 forms of procarboxypeptidase B differ from each other mainly in isoelectric point.The deduced amino acid sequence of PCPB predicts a 416-amino acid preproenzyme consisting of a 15-aa signal peptide, a 95-aa activation peptide and a 307-aa mature chain. The secreted PCPB zymogen is converted to enzymatically active CPB1 by limited proteolysis by trypsin.
Carboxypeptidase B2 (CPB2) is a secreted enzyme that belongs to the peptidase M14 family. CPB2 is synthesized by the liver and circulates in the plasma as a plasminogen-bound zymogen by the liver and circulates in the plasma as a plasminogen-bound zymogen. CPB2 cleaves C-terminal arginine or lysine residues from biologically active peptides, such as kinins or anaphylatoxins, in the circulation regulating their activities. CPB2 also down-regulates fibrinolysis by removing C-terminal lysine residues from fibrin that has already been partially degraded by plasmin. CPB2 exhibits carboxypeptidase activity when it is activated by proteolysis at residue Arg92 of the thrombin/thrombomodulin complex. Activated CPB2 reduces fibrinolysis by removing the fibrin C-terminal residues that are important for the binding and activation of plasminogen.
Carboxypeptidase B2, also known as Carboxypeptidase U, Thrombin-activable fibrinolysis inhibitor, Plasma carboxypeptidase B, CPB2, is a secreted protein which belongs to the peptidase M14 family. Carboxypeptidases are enzymes that hydrolyze C-terminal peptide bonds. The carboxypeptidase family includes metallo-, serine, and cysteine carboxypeptidases. According to their substrate specificity, these enzymes are referred to as carboxypeptidase A (cleaving aliphatic residues) or carboxypeptidase B (cleaving basic amino residues). CPB2 is activated by thrombin and acts on carboxypeptidase B substrates. After thrombin activation, the mature protein downregulates fibrinolysis. CPB2 is synthesized by the liver and circulates in the plasma as a plasminogen-bound zymogen. When it is activated by proteolysis at residue Arg92 by the thrombin / thrombomodulin complex. CPB2 cleaves C-terminal arginine or lysine residues from biologically active peptides such as kinins or anaphylatoxins in the circulation thereby regulating their activities. CPB2 exhibits carboxypeptidase activity and activated CPB2 reduces fibrinolysis by removing the fibrin C-terminal residues that are important for the binding and activation of plasminogen.
Carboxypeptidase E (CPE), also known as Carboxypeptidase H, is a peripheral membrane protein and a zinc metallocarboxypeptidase, and the conversion of proCPE into CPE occurs primarily in secretory vesicles. The active form of CPE cleaves C-terminal amino acid residues of the peptide, and is thus involved in the biosynthesis of peptide hormones and neurotransmitters including insulin, enkephalin, etc. The enzymatic activity is enhanced by millimolar concentrations of Co2+. It has also been proposed that membrane-associated carboxypeptidase E acts as a sorting receptor for targeting regulated secretory proteins which are mostly prohormones and neuropeptides in the trans-Golgi network of the pituitary and in secretory granules into the secretory pathway.Its interaction with glycosphingolipid-cholesterol rafts at the TGN facilitates the targeting. Mutations in this gene are implicated in type II diabetes due to impaired glucose clearance and insulin resistance.
The active form of CPE cleaves C-terminal amino acid residues of the peptide, and is thus involved in the biosynthesis of peptide hormones and neurotransmitters including insulin, enkephalin, etc. It is thought that membrane-associated CPE acts as a sorting receptor for targeting regulated secretory proteins which are mostly prohormones and neuropeptides in the trans-Golgi network of the pituitary and in secretory granules into the secretory pathway. Defects in this protein are implicated in type II diabetes due to impaired glucose clearance and insulin resistance.
Carboxypeptidase M (CPM) specifically removes C-terminal basic residues (Arg or Lys) from peptides and proteins. Carboxypeptidase exert roles in the physiological processes of blood coagulation/fibrinolysis, inflammation, food digestion and pro-hormone and neuropeptide processing. CPM is believed to play important roles in the control of peptide hormone and growth factor activity at the cell surface, and in the membrane-localized degradation of extracellular proteins. It is widely distributed in a variety of tissues and cells. CPM is involved in peptide metabolism on both the cell surface and in extracellular fluids. CPM functions not only as a protease but also as a binding partner in cell-surface protein-protein interactions.
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