Protamine inhibits formation of the covalent factor IXa-anti-thrombin complex.

The effect of protamine sulfate upon the covalent interaction of human factor IXa with anti-thrombin has been investigated by a quantitative SDS-polyacrylamide gel electrophoresis procedure. Protamine sulfate inhibits the interaction of factor IXa with anti-thrombin upon preincubation with factor IXa, anti-thrombin, or a mixture of the two components. As a consequence of the presence of protamine sulfate, autolysis of factor IXa is promoted to generate a degradation product of a molecular weight (apparent) of 35 kDa.