You are examining the processes of blood coagulation utilizing in vitro assays involving the addition of potential inhibitory compounds. In your control assay the rate of fibrin clot formation, following addition of whole blood, takes 16 seconds. The addition of your compound results in fibrin clot formation in 3 seconds. Given the observed results, which of the following proteins is most likely targeted for inhibition by the test compound?

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Protein C (PC) is a trypsin-like serine protease that serves as a major regulator of the coagulation process. Thrombin cleavage of PC removes the activation peptide generating aPC. When activated through cleavage by thrombin, aPC cleaves both factor Va and factor VIIIa into inactive enzymes. This results in the termination of the role of VIIIa as the scaffold for the formation of the tenase complex and Va as a cofactor in the conversion of prothrombin to thrombin in the prothrombinase complex. The net effect, at the level of coagulation, of the activation of PC is termination of further increases in thrombin production and a halt to further fibrin clot formation. A lack of aPC activity would be apparent if fibrin clotting was accelerated due to lack of inhibition of factors Va and VIIIa

You Are Examining the Processes of Blood Coagulation Utilizing in Vitro