The effect of sulfation on the anticoagulant and antithrombin III-binding properties of a heparin fraction with low affinity for antithrombin III

Abstract

Heparin with low affinity for antithrombin III (ATIII) and devoid of anticoagulant activity was chemically oversulfated and fractionated by affinity for ATIII. The oversulfated material showed ATIII binding properties, as monitored by intrinsic fluorescence enhancement of ATIII. The fluorescence increase was comparable to that of the AT III high affinity fraction of native heparin. The estimated dissociation constants however, showed a 10-fold weaker binding of the oversulfated material to ATIII, K d = 6.4 × 10 −8 M, as compared to native heparin, K d = 0.63 × 10 −8M. Concomitant with the binding-induced allosteric change in ATIII, the oversulfated material stimulated the ATIII-thrombin and ATIII-factor Xa reactions. The high affinity fractions of native heparin and the sulfated material were almost equally effective in enhancing the rate of thrombin neutralization by ATIII. However, a 3-fold faster rate of factor Xa inactivation was found with the native high affinity material.