ROLE OF FACTOR-VIII AND FACTOR-IX IN THE ACTIVATION OF BOVINE BLOOD-COAGULATION FACTOR-X

The exterase activity of bovine Factor Xa on the synthetic substrate α-N-benzoyl-L-arginine ethyl ester was used to follow the activation of Factor X by the intrinsic pathway of coagulation. Factor IXa alone activated Factor X in a calcium-dependent reaction. The rate of the reaction was enhanced by Factor VIII, which did not activate Factor X in the absence of Factor IXa. A further stimulation of the rate of activation of Factor X was obtained when phospholipid was added to the system, although there was not an absolute requirement for exogenous phospholipid. Hirudin had no effect on the rate of activation of Factor X in the absence of Factor VIII, but markedly reduced the stimulatory effect of Factor VIII. © 1979.