Experimental proof for the structure of a thrombin-inhibiting heparin molecule

Kinetic studies of thrombin inhibition by antithrombin in the presence of h eparin have shown that thrombin binds to heparin in a preformed heparin - a ntithrombin complex. To study the relative position of the thrombin binding domain and the antithrombin binding domain on a heparin molecule we have d esigned and synthesized heparin mimetics which structurally are very simila r to the genuine polysaccharide. Their inhibitory properties with respect t o factor Xa and thrombin provide experimental evidence that in heparin the thrombin binding domain must be located at the nonreducing end of the antit hrombin binding domain to observe thrombin inhibition. As expected, factor Xa inhibition is not affected by elongation of the antithrombin binding pen tasaccharide sequence, regardless of the position in which this elongation takes place.