The rate of inactivation of factors IX a and VIII as well as of the complex formed
by them on the surface of platelets, induced by specific inhibitors has been studied.
After the formation of complex both factors became more protected against high molecular
weight inhibitors. As evidenced by the apparent first order inactivation rate constants,
after complex formation the velocity of IX a – antithrombin III + heparin reaction
fell to one-fourth, that of factor VIII – VIII : C antibody reaction decreased to
1/20. Enhanced resistance toward the high molecular weight inhibitors is presumably
due to a steric change, since the low molecular weight phenylmethyl sulfonyl fluoride
and diethyl pyrocarbonate inhibited free and complexed factor IX a to the same extent.
Key words
Factor IX a - Factor VIII - Platelets - Antithrombin III - Factor VIII: C antibody
