Abstract
Results of uv-difference spectroscopy and steady-state inhibition measurements indicate that proflavin binds to thrombin ( K i ⋍1.0×10 −5 m ) with 1:1 stoichiometry and in such a way as to compete with substrates and benzamidine for access to the active site region. The use of a clotting assay demonstrates that proflavin inhibits the thrombin-fibrinogen interaction. Proflavin concentrations of 7±2×10 −5 m approximately double the clotting time. Hirudin binds tightly to thrombin, as judged from an active-site titration assay, and displaces proflavin from the enzyme. pH-Jump experiments indicate that thrombin does not undergo a pH-dependent active-inactive conformational equilibrium such as that seen for α -chymotrypsin. Preliminary results of stopped-flow experiments for the interaction between thrombin-proflavin complex and the N-disulfide knot of fibrinogen are described.
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