Demonstration of a direct anti-factor Xa activity in certain heparin-related glycosaminoglycans.

Heparan sulphate/heparin subfractions with high plasma anti-Xa activity have an unusual uronate composition, i.e. high proportions of both glucuronate and sulphated iduronate. These preparations inhibit the amidase activity of factor Xa in an uncompetitive mode and the prothrombin-activation catalyzed by Xa, both in the absence of antithrombin III. Subfractions of low affinity for antithrombin III are equally potent against Xa. The anti-X activity is destroyed by a 3-h periodate oxidation.