Kenton Hicks, Kyle Stucker, Allen Betts

Trypsin is serine protease which catalyzes the hydrolysis of peptide bonds of a substrate via an acylation reaction and a deacylation reaction. In the first (acylation) reaction, the nucleophilic serine attacks the substrate scissile bond, forming a tetrahedral intermediate and then a covalent acyl-enzyme with the release of the C-terminal fragment. In the second (deacylation) reaction, a water molecule attacks the acyl-enzyme, leading to a second tetrahedral intermediate followed by release of the N-terminal fragment. The active site of the enzyme that catalyzes the reaction contains the residues Ser 195, His 57, and Asp 102. These three residues make up the . An is specifically formed between the amide hydrogen atoms of Serine 195 and Glycine 193. This oxyanion hole stabilizes the tetrahedral intermediate through the distribution of negative charge to the cleaved amide. The specificity of substrates is determined by the structure of its . The preference for lysine or arginine in trypsin catalysis is due to the composition of the trypsin specificity pocket. Asp 189 and one of two significant glycine backbones, Gly 216, interact with the ligand as they would with Arg or Lys.

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