LMWH binds to anti-thrombin, a serine protease inhibitor, and creates a conformational change. This change accelerates its inhibition of activated factor X in conversion of prothrombin to thrombin. Thus,thrombin cannot convert fibrinogen to fibrin strands and clot formation. Once this change occurs LMWH is freed and can bind to another anti-thrombin molecules. LMWH also directly inhibits thrombin as it is a heterogenous mixture of molecules, some containing enough polysaccharide sequence, but this effect is much less than that of unfractionated heparin.