Measurement of carboxypeptidase R by colorimetric assay

Carboxypeptidases (CP), carboxypeptidase N (CPN) and carboxypeptidase R (CPR), have been reported as a protease, which can cleave carboxy-terminal arginine or lysine residues from biologically active peptides, such as C3a and C5a, and regulate their activity. CPN is present in the active form in plasma, but CPR is generated from its zymogen during coagulation. CPR (identical to carboxypeptidase U [CPU], plasma carboxypeptidase B [plasma CPB]) has also been described as an inhibitor of fibrinolysis, and termed TAFI (thrombin activatable fibrinolysis inhibitor). ProCPR is activated by thrombin, thrombin-thrombomodulin complex (T-TM), plasmin, and trypsin. Today, the T-TM complex pathway has been taken notice because of effectiveness of Protein C for sepsis. Protein C has been recognized as a mediator between inflammation and coagulation. About CPR, some recent clinical studies have been shown that CPR is an acute phase protein and proCPR have been reduced in DIC. Similar to Protein C, CPR may be a mediator between inflammation and fibrinolysis. Colorimetric assay is one of the methods for measuring CP activity. Although it is convenient for determining CP activity, we noticed that some anticoagulants, such as citrate, interfere with the color development of the reagents used. Therefore, concentration of citrate in samples should be controlled to be constant for background subtraction. If one will pay attention to this point, colorimetric assay will be a good method for measuring CP activity and give us further findings.