The<unk>  complex consists of the serine protease, Factor Xa, and the protein cofactor, Factor Va. The complex assembles on negatively charged phospholipid membranes in the presence of calcium ions. The<unk>  complex catalyzes the conversion of prothrombin (Factor II), an inactive zymogen, to thrombin (Factor IIa), an active serine protease. The activation of thrombin is a critical reaction in the coagulation cascade, which functions to regulate hemostasis in the body. To produce thrombin, the<unk>  complex cleaves two peptide bonds in prothrombin, one after Arg271 and the other after Arg320. Although it has been shown that Factor Xa can activate prothrombin when unassociated with the<unk>  complex, the rate of thrombin formation is severely decreased under such circumstances. The<unk>  complex can catalyze the activation of prothrombin at a rate 3 x 105-fold faster than can Factor Xa alone. Thus, the<unk>  complex is required for the efficient production of activated thrombin and also for adequate hemostasis.
Prothrombinase
Thrombin
Platelet-activating factor
Factor VIII 
Factor VIII
Von Willebrand factor
Factor XI
Factor IX