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?
Answer Options:O A to EO A to KO A to SO A to MO A to Y

O. A to K

Explanation:

Arginine (R) is a positively charged basic amino acid and alanine (A) is a hydrophobic amino acid. Arginine is mostly found on surface of protein to produce hydrogen bonds or other ionic combinations so as to provide stability to the protein or control the activity of the protein. Alanine on the other hand, is hydrophobic. Thus, when arginine is replaced with alanine the catalytic ability of the enzyme are affected.

Lysine (K) is known to be a positively charged basic amino acid like arginine. Therefore, mutating alanine to lysine will confer the chemical abilities of the protein as a result of similarity in chemical attributes of arginine and lysine, which will confer the wild type characters of the enzyme.