The functional domain of hirudin, a thrombin-specific inhibitor.

Hirudin is a thrombin-specific inhibitor of Mr 8000 (65 amino acid residues). Native hirudin contains 3 disulfide linkages within the first 39 amino-terminal residues, and a highly acidic C-terminal segment which is freely accessible to enzyme digestion by both endo- and exo-peptidases. Removal of the acidic C-terminal amino acids of native hirudin by both chemical and enzymatic methods resulted in a concomitant loss of hirudin inhibition activity. It is concluded that this acidic C-terminal segment of hirudin is essential for hirudin-thrombin interaction. The implication of the hirudin-thrombin interaction for the enzymatic specificity of thrombin is also discussed.