Kinetics of human factor VII activation

The membrane bound factor Xa appears to be the major activator of the vitamin K dependent zymogen, human factor VII, in vivo. The activation by Xa is anionic phospholipid (PCPS) dependent. The VIIa-tissue factor complex (factor IXa) and thrombin activate factor VII in vitro, but in vivo activation is uncertain. In the presence of PCPS, factor VIIIa has no affect on the activation by factor IXa, while factor Va decreases the activation by Xa. Factor XIa has no observable effect on factor VII activation rates.