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Download Mechanism of action of trypsin and chymotrypsin
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Transcript
Mechanism of action of trypsin and chymotrypsin • In the digestive system, trypsin, chymotrypsin and elastase work as a team. • All are endopeptidases, which means that they cleave protein chain at internal peptide bonds adjacent to particular type of amino acids. Specificity • In both trypsin and chymotrypsin, the side chain of substrate fits into a pocket. At the far end of this pocket. • In trypsin there is negatively charged aspartic acid residue which tends to bind through COO- group to the positively charged side chain of lysine and arginine. • Trypsin cuts next to basic amino acid residues e.g lysine or arginine. • Chymotrypsin cuts just to aromatic residues as phenyl alanine, tyrosine and tryptophane. • Elastase preferes small hydrophobic residues like alanine. • Trypsin, Chymotrypsin and elastase are structurally similar (i.e have similar crystal structure). • Small set of amino acid residues come together in the folded structure to be essential of the active site catalysis. These are: - His 57 -Asp 102 - Ser 195 • Studies show that the reactivity of ser 195 is not due to a property of serine residue itself but depends on the special surroundings of this residue which is His 57 and aspartic 102. which make serine specially reactive. • Histidine 57 sits nearby, in an orientation suggesting that OH group of ser 195 forms hydrogen bond with the imidazole side chain. • Aspartic acid sits in the opposite site of the imidazole ring, where the negatively charged carboxylic group can interact with the hydrogen proton on the nitrogen of the ring. This orientation helps the removal of the proton from serin’s OH group. Mechanism Detailed mechanism will be illustrated on the board to be more clear