Consider a protein with two surface-exposed histidine residues:HisA is a “typical” histidine residue with a pKa = 6.2HisB is involved in a stabilizing interaction (His-NH+ ..... -O2C-Glu) with a neighboring glutamic acid residue. For HisB, the Gibbs free energy of deprotonation at pH = 7.0 and T = 293K is ΔG'o = +15 kj mol-1.If you had a solution, at pH = 7.0 and T = 293K, containing this protein:a) What fraction of HisA residues are protonated?b) What fraction of HisB residues are protonated?c) What is the pKa of HisB?

The Henderson-Hasselbalch equation for the deprotonation of a species is given…

Answered: Consider a protein with two…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Consider a protein with two surface-exposed histidine residues:

His_A is a “typical” histidine residue with a pKa = 6.2
His_B is involved in a stabilizing interaction (His-NH⁺ ..... ^-O₂C-Glu) with a neighboring glutamic acid residue. For His_B, the Gibbs free energy of deprotonation at pH = 7.0 and T = 293K is ΔG'^o = +15 kj mol-1.

If you had a solution, at pH = 7.0 and T = 293K, containing this protein:

a) What fraction of His_A residues are protonated?

b) What fraction of His_Bresidues are protonated?

c) What is the pKa of His_B?

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