Antithrombin Rouen‐IV 24 Arg→Cys The amino‐terminal contribution to heparin binding

Abstract
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 Å 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.