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 is available for your reference. Determine which specificity pocket is a part of each enzyme.

1. charge in trypsin

: two other molecules in elastase

2. Chymotrypsin cleaves peptide bonds after bulky or aromatic side chains, such as those of the amino acids phenylalanine or tyrosine. The specificity pocket, or substrate-binding site, is deep and has hydrophobic side chains.

Trypsin cleaves peptide bonds following basic amino acid side chains. Lysine and arginine both have basic amino acid side chains that are positively charged at pH 7. Trypsin's substrate-binding site contains a negatively charged amino acid residue.

Elastase cleaves peptide bonds after amino acids with small side chains, such as glycine, alanine, or valine. The specificity pocket for elastase has bulky side chains that block larger amino acid side chains, but can accomodate smaller side chains, such as the - H, - CH3, and - CH (CH3) 2 side chains of glycine, alanine, and valine, respectively.

3. Their binding pockets

trypsin = long & (-) D on bottom chymotrypsin = deep & wide elastase = aliphatic a. a. = shallow