Question

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?

a. A to M
b. A to S
c. A to K
d. A to Y
e. A to E

Answer 1

The most likely mutation to restore wild-type activity is A to K. Histidine is an amino acid that can form a similar type of interaction in the active site of an enzyme.

Step-by-step explanation:

The most likely mutation to restore a wild-type level of activity to the alanine mutant is A to K. The conversion of alanine to lysine introduces a positively charged amino acid, similar to arginine. This positive charge may help restore the critical catalytic function in the active site of the enzyme.

An amino acid that might form a similar type of interaction in the active site of an enzyme is histidine. Histidine has a positively charged side chain at physiological pH and can participate in hydrogen bonding and acid-base catalysis.

Answer 2

c. A to K

Step-by-step explanation:

If the alanine mutation is restored to K or lysine residue, most likely the wild type level of activity can be restored. This is because, arginine and lysine have -NH2 as the functional group. So, functional similarity of arginine can be expected from lysine as well.

Hence the correct option is c that is A to K.