Answer:
A to N
Explanation:
Glutamine is an amino acid with a polar, uncharged side chain. The mutation to alanine, an amino acid with a non-polar side chain, completely affects the enzymatic activity. This makes sense considering the difference in the nature of both amino acids.
To restore the wild-type level of activity the alanine would have to mutate to another polar uncharged amino acid. Among the given options, only Asparagine (N) has a similar chemistry to Glutamine.