Study on complex formation between recombinant human thrombomodulin fragment and thrombin using surface plasmon resonance

Human thrombomodulin (hTM) is a newly described endothelial cell associated protein that functions as a potent natural anticoagulant by converting thr ombin from a procoagulant protease to an anticoagulant. The affinity consta nt of recombinant human soluble TM (rhs-TM) and a peptide containing active site of hTM fragment (f-hTM) with thrombin were determined using the surfa ce plasmon resonance. The interaction of f-hTM with thrombin could be analy zed by a simple model, whereas the association and the dissociation steps o f rhs-TM with thrombin consisted of at least two kinds of interaction phase s. The dissociation constant for complex (K-D) of f-hTM and thrombin was de termined to be 205 nM, which was more than twice as high as that of rhs-TM (6.7 and 75 nM), The lower affinity of f-hTM was not due to the slow associ ation rate but to the rapid dissociation rate. It comes clear that f-hTM in teracts with thrombin rapidly. Am. J. Hematol, 63:136-140, 2000. (C) 2000 W iley-Liss, Inc.