Human factor VII is a single chain plasma glycoprotein, and is a zymogen in its native form. Proteolytic activation of factor VII, yields the enzyme factor VIIa, which when bound to the integral membrane protein tissue factor, forms an enzyme complex that proteolytically converts factor X to factor Xa. This enzyme complex is best known as the extrinsic factor Xase (pronounced ten-ase) complex, since by virtue of its tissue factor component, it is composed of protein normally extrinsic to the plasma environment. The conversion of factor VII to factor VIIa is catalyzed by a number of proteases including thrombin, factor IXa, factor Xa, factor XIa, and factor XIIa. Rapid activation also takes place when factor VII is combined with tissue facto