Antithrombin Rouen-IV 24 Arg----Cys. The amino-terminal contribution to heparin binding

A variant antithrombin with reduced heparin affinity was shown by mass spectrometry sequencing and DNA amplification to have a substitution of a cysteine for an arginine at residue 24. The position of Arg-24 can be fixed within a 12 A radius from the bridge at Cys-21. This is compatible with findings in the homologous protease nexin-1 which indicate an extension of the binding site of heparin from the D-helix to under the adjacent amino-terminal pole.