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.
Which of the following amino acids have side chains that fit into the specificity pocket of chyrmotrypsin?

a. glycine
b. arginine
c. phenylalanine
d. alanine
e. aspartate
f. tyrosine

Answer 1

Answer:

The correct options are:

c. phenylalanine

f. tyrosine

Explanation:

The specificity of the pocket of chymotrypsin is for aromatic aminoacids o amino acids with bulky hydrophobic chains. From the list of amino acids, the aromatic amino acids are phenylalanine (with a phenyl group) and tyrosine (with a phenolic group).

From the rest, there are not amino acids with bulky hydrophobic side chains. Arginine has a 3-carbon side chain but it has a polar guanidino group, so it is not a bulky hydrophobic R-group. Alanine is hydrophobic but it is not bulky - it has only a methyl (-CH₃) group as R-group. Aspartate is not hydrophobic neither aromatic. Finally, glycine is very simple, it has only a -H as R-group.