The molecular-weight dependence of the rate-enhancing effect of heparin on the inhibition of thrombin, factor Xa, factor IXa, factor XIa, factor XIIa and kallikrein by antithrombin

Abstract

Heparin fractions [from pig mucosa] of different MW and with high affinity for [human] antithrombin were studied with respect to their ability to potentiate the inhibition of activated clotting factors by antithrombin. Inhibition of [bovine] thrombin, factor IXa and factor XIa showed similarities in the dependence on the MW of heparin and decreased with decreasing MW. Inactivation of factor Xa, factor XIIa and kallikrein was less dependent on the size of the polysaccharide and, to a great extent, was potentiated even by low MW heparin fractions that had virtually no effect on the inhibition of thrombin factor IXa and factor XIa.