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.