Time-dependent conformational change of thrombin molecules induced by sulfated polysaccharides.

Dextran sulfate (DS) had a greater ability to elute thrombin adsorbed on a small Sepharose 6B column than heparin did, while chondroitin sulfate A had little ability. It is probable that the strength of the interaction of thrombin depends mostly on the charge-density of strongly acidic sulfate groups in the polysaccharides. The change in intrinsic fluorescence intensity of thrombin with time was closely correlated with the rate of inactivation of the enzyme in the presence of sulfated polysaccharides. Both rates were affected by the pH of the solution in the presence of the polyanions. The rates in the presence of DS were highest at pH 6.05 among the three pHs tested, while they were enhanced only at pH 6.05 by heparin, but not by chondroitin sulfate A. Therefore, extensive charge-neutralization of thrombin by the sulfated polysaccharides is able to induce time- and temperature-dependent intramolecular conformational change (irreversible denaturation) of the enzyme molecules.