Hirudin: Hirudin is a potent thrombin inhibitor originally derived from the medicinal leech Unlike heparin, hirudin act directly on thrombin, rather than through other clotting factors. They have a high binding affinity and specificity for thrombin. The mechanism of hirudin-thrombin binding appears to be unique. Recombinant hirudin variant is derived from yeast cell, the polypeptide containing 65 amino acid residues has a molecular weight of 6979.5 Da, which is identical to natural hirudin except for substitution of leucine for isoleucine at the N-terminal end of the molecule and the absence of a sulfate group on the tyrosine at position 63. UnitProt ID: P84590