Inactivation
Factor Va is inactivated following cleavage by activated protein C. Activated protein C cleaves Factor Va in both its light and heavy chains. Cleavage in the heavy chain reduces the ability of Factor V to bind to Factor Xa. Activated protein C interacts tightly and exclusively with the light chain of Factor Va, and this interaction is calcium independent. Factor Xa can help to prevent the inactivation of Factor Va by protecting Factor Va from activated protein C. It is likely that Factor Xa and activated protein C compete for similar sites on Factor Va. Factor Xa is inhibited by the antithrombin III/heparin system, which also acts to inhibit thrombin.
Read more about this topic: Prothrombinase