Antithrombin activity of the hirudin N-terminal core domain residues 1–43

Hirudin N-terminal core domain residues 1–43 (r-Hir^1–43) were prepared from limited proteolysis of recombinant hirudin by V8 Staphylococcal protease followed by purification with reversed-phase HPLC. r-Hir^1-43 lacks the putative reactive site of hirudin (Lys⁴⁷), but binds to thrombin (with K_i of 300 nM) and blocks the catalytic activity of the protease. The structural element which accounts for the thrombin inhibitory activity of r-Hir^1–43 is analyzed in this report.