Structure and biological activity of finback-whale (Balaenoptera physalus L.) heparin octasaccharide. Chemical, carbon-13 nuclear-magnetic-resonance, enzymic and biological studies

Abstract

Finback-whate (B. physalus) heparin was partially digested with a purified heparinase and an octasaccharide with high affinity for antithrombin III was isolated from the digest by gel filtration, followed by affinity chromatography on a column of antithrombin III immobiized on Sepharose 4B. This octasaccharide possessed high inhibitory activity for factor Xa in the presence of antithrombin III but was essentially inactive for thrombin-antithrombin III reaction. The anticoagulant activity determined by the activated-partial-thromboplastin-time method was very low (40-70 U/mg), although the initial whale heparin exhibited high activity (252 U/mg). On the basis of the results of chemical analyzes, 13C NMR spectrum and enzymic studies with purified heparinase, heparitinases 1 and 2, the predominant structure of the octasaccharide was proposed as follows: .DELTA.UA(2S).alpha.1 .fwdarw. 4GlcNS.alpha.1 .fwdarw. 4IdUA.alpha.1 .fwdarw. 4GlcNAc(6S).alpha.1 .fwdarw. 4GlcUA.beta.1 .fwdarw. 4GlcNS(3S).alpha.1 .fwdarw. 4IdUA(2S).alpha.1 .fwdarw. 4GlcNS. Comparing this structure with those of the heparin octasaccharides so far reported, the presence of the critical structural elements for bindig to antithrombin III was suggested in the pentasaccharide region situated at the reducing end of this octasaccharide. Binding to antithrombin III of the critical structural elements alone would appear to elicit the acceleration of the factor Xa-antithrombin III reaction. Additional structural elements required for the acceleration of the thrombin-antithrombin III reaction and for the manifestation of high anticoagulant activity are discussed.