Final answer:
The specificity pocket change from chymotrypsin to that of elastase is achieved by substituting a bulky amino acid for a smaller one, which in this case is (d) Isoleucine to Valine.
Step-by-step explanation:
The specificity pocket change from chymotrypsin to that of elastase is accomplished by an amino acid substitution that reduces the size of the pocket to only accommodate small amino acids such as Ala or Gly. Chymotrypsin typically has a large specificity pocket that allows it to bind to aromatic amino acids such as phenylalanine, tyrosine, and tryptophan. The substitution that would change the specificity pocket of chymotrypsin to resemble that of elastase's smaller pocket is the substitution of a bulky amino acid for a smaller one.
Given the options provided in the question:
- (a) Glycine to Alanine
- (b) Serine to Threonine
- (c) Tyrosine to Phenylalanine
- (d) Isoleucine to Valine
The correct answer is (d) Isoleucine to Valine. Isoleucine has a bulkier side chain than valine, and substituting it for valine would create a smaller specificity pocket similar to that of elastase.