Imagine an enzyme that needs a deprotonated Aspartic Acid an

Imagine an enzyme that needs a deprotonated Aspartic Acid and a protonated Tyrosine. At which of the following pH values, would the enzyme work best?

A. pH = 2

B. pH = 4

C. pH = 8

D. pH = 12

Solution

Answer: C. pH = 8

pKa of Tyrosine side chain is 10, and for aspartic acid is 3.8.

Below the pH 10, the tyrosine mostly protonated. Above pH 3.8 Aspartic acid exists predominantly in deprotonated form.

So = (3.8 +10)/2 = 6.9

So at pH value ~6.9

Close value given is pH 8