ABSTRACT
Thrombin is a regulatory tryptic-like serine protease functioning in hemostasis, wound healing, and other regulatory functions. A regulatory protease differs from a digestive protease in that a regulatory protease will cleave only a limited number of the potentially susceptible peptide bonds in a protein, while a digestive protease would cleave most, if all, peptide bonds, an exception being a peptide bond containing proline. In the cleavage of peptide bonds, it is likely that the process of acylation of the active serine residue via the formation of a tetrahedral intermediate is the rate-limiting step and would depend, in part, on the nucleophilicity of the serine residue. The active-site serine residue S205 in thrombin can be modified with DFP, resulting in a total loss of enzymatic activity. The participation of a histidine residue in the catalytic function of thrombin can be inferred by homology to chymotrypsin and trypsin, where early studies suggested participation of a histidine residue.
