Determination of functional levels of protein C, an antithrombotic protein, using thrombin-thrombomodulin complex.
Protein C is a vitamin K-dependent plasma protein. Activated protein C is a potent anticoagulant and enhances blood clot lysis. We have developed a functional assay for protein C in human plasma. The measurement of protein C is accomplished by the addition of thrombomodulin, an endothelial-cell-associated cofactor for protein C activation, and thrombin in a 1:1 molar complex. The activated protein C formed in the plasma is immunoadsorbed with goat anti-human protein C IgG-agarose. The immunoadsorbed activated protein C retains the ability to hydrolyze chromogenic substrates, and after unbound plasma proteins are removed by washing, the bound activated protein C is quantitated by incubation with the substrate H-D-phe-pip-arg-p-nitroanilide (S-2238). Normal individuals have functional protein C levels of 3.9-5.9 micrograms/ml, with a mean value of 4.8 micrograms/ml. Individuals undergoing warfarin anticoagulation and patients with advanced liver diseases have decreased levels, as do certain patients with evidence of intravascular clotting. Functional protein C levels correlate well with immunologic levels of the protein in the patient groups studied. Heparin enhances the rate of activated protein C inhibition, as monitored by recovery of activated protein C by immunoadsorption. A patient with recurrent venous thrombosis and abnormal functional protein C activity, but normal levels of antigen, has been identified.
D000328:Adult; D000818:Animals; D001777:Blood Coagulation / Q000187:drug effects; D001780:Blood Coagulation Tests / Q000379:methods; D006023:Glycoproteins / Q000032:analysis* / Q000378:metabolism / Q000502:physiology; D006041:Goats; D006493:Heparin / Q000627:therapeutic use; D006801:Humans; D007163:Immunosorbent Techniques; D008103:Liver Cirrhosis / Q000097:blood; D008297:Male; D008875:Middle Aged; D011486:Protein C; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000378:metabolism / Q000502:physiology; D018179:Receptors, Thrombin; D013917:Thrombin; D013924:Thrombophlebitis / Q000097:blood / Q000188:drug therapy; D014859:Warfarin / Q000627:therapeutic use
D006023:Glycoproteins; D011486:Protein C; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D014859:Warfarin; D006493:Heparin; D013917:Thrombin