The effect of polycations on the inhibitory action of antithrombin III on thrombin in the absence and presence of polyanions.

Polycations of biological and synthetic origin inhibit the action of AT III on thrombin activity. The effect is more pronounced with increasing molecular weight of branched polycations. Quantitatively protamine causes the same effect as quaternized polycations on the basis of charge equivalence. The accelerating effect of heparin or potassium polyvinylsulfate for the inhibitory action of AT III is abolished by charge equivalent amounts of polycation. The observations indicate a dual action of polycations in the heparin/AT III/thrombin interaction.