Question

Classify each amino acid according to whether its side chain is predominantly protonated or deprotonated at a pHpH of 7.40.7.40. The pKapKa values of the Asp, His, and Lys side chains are 3.65, 6.00, and 10.53,3.65, 6.00, and 10.53, respectively.

Answer 1

Answer: His and Lys are deprotonated but Asp will be protonated.

Explanation:

As the pH is given as 7.4 and pK of His is given as 6.00. There will occur a positive charge on His when it's pH < pK therefore, it is neutral at the given pH.

As the pK value of Lys is 10.53 that is greater than the pH of 7.40. Therefore, charge on Lys is positive.

As the pK value of Asp is 3.65 which is less than the pH value of 7.40. Hence, Asp has a negative charge.

Therefore, we can conclude that His and Lys are deprotonated but Asp will be protonated.