Suppose that an arginine residue in the active site of an enzyme was mutated to alanine. as expected, the alanine mutant was inactive, suggesting that the arginine residue was critical to the catalytic mechanism. which mutation is most likely to restore wild-type level of activity to the alanine mutant?

1. a to e
2. a to k
3.a to s
4.a to m
5.a to y

2. A to K

Explanation:

Arginine (R) is a positively charged basic amino acid whereas alanine (A) is a hydrophobic amino acid. Arginine is usually present on surface of protein to form hydrogen bonds or other ionic interactions to confer stability to the protein or influence the activity of the protein. Alanine being hydrophobic is usually buried within the protein core. Hence when arginine is substituted with alanine the catalytic properties of the enzyme are disturbed.

Lysine (K) is also positively charged basic amino acid like arginine so if alanine is mutated to lysine the chemical properties of the protein will be restored most probably because of similarity in chemical nature of arginine and lysine, which will restore the wild type activity of enzyme.

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