ANTITHROMBIN AND HEPARIN

Antithrombin, the main inhibitor of thrombosis in blood, is bound and activated by the heparin-like side-chains that line the small vasculat ure. We now have good depictions of the heparin-binding site on antith rombin, and of the way in which mutations at this site cause thromboti c disease. The interaction of heparin with antithrombin is, however, a kinetic one, with binding being followed by formation of a complex wi th thrombin and then release from the heparin. Our understanding of th e processes involved is currently based on crystallographic models but , for a mobile mechanism, these merely provide snapshots - what is nee ded is a movie.