At what pH value would you expect the electrostatic attracti

At what pH value would you expect the electrostatic attraction (charge attraction) between the side chains of histidine (pKa=6.5) and glutamic acid (pKa=4.25) in a protein to be strangest?

a. 10

b. 7

c. 5.5

d. 3

e. should be the sam at all pH values

I know that the answer is 5.5, but please explain why and how I could find this if I were given two other amino acids.

Solution

Answer:

pKa value is the the pH at which half of the ionizable groups are ionized.

histidine (pKa=6.5) and glutamic acid (pKa=4.25)

At the pKa intermediate between 6.5 and 4.25 we find more positive and more negative groups hence electrostatic attraction (charge attraction) is expected.

=(6.5+4.25)/2

= 5.4