Chymotrypsin, trypsin, and elastase are digestive enzymes called serine protease
ID: 94868 • Letter: C
Question
Chymotrypsin, trypsin, and elastase are digestive enzymes called serine proteases. The serine proteases differ in substrate specificity: Chymotrypsin cleaves peptide bonds after aromatic or bulky hydrophobic side chains: trypsin requires basic amino acid residues: and elastase cleaves bonds following small uncharged side chains. A chart of amino acids can be found here. The specificity pockets (substrate-binding sites) of each of the serine proteases are drawn below. The substrate amino acid side chains are shown in each pocket. (a) Determine which specificity pocket is a part of each enzyme. Move each specificity pocket, below, to the proper bin. (b) Which of the following amino acids have side chains that fit into the specificity pocket of trypsin? Select all the amino acids that fit. You will need to check more than one amino acid. lysine arginine phenylalanine aspartate glycine alanineExplanation / Answer
a. The third one specificity pocket (elastase) is a part of each enzyme. Elastase specificity pocket has small uncharged side chains which is common to all the three. Specificity pocket for chemotrypsin has shape suitable for fitting a aromatic ring which has a small uncharged side chain. Trypsin has two long charged side chain and the last portion of this long charged side chains can be considered as small uncharged side chain. Hence all the three specificity pocket has the shape suitable for fitting with small uncharged side chain as in elastase specificity pocket.
b. Since trypsin require basic amino acid residues, the amino acids which have basic amino acid residues will fit into the specificity pocket of trypsin. Only Lysine and arginine out of given amino acids have the basic side chains at neutral pH. Hence the answer will be lysine and arginine.