Let's consider a protein with two surface-exposed histidine residues: • Hisa is a "typical" histidine residue with pK = 6.2 • Hisg is involved in a stabilizing interaction (His-NH* --- -0,C-Glu) with a neighboring glutamic acid residue. For Hisg, the Gibbs free energy of deprotonation at pH = 7.0 and T = 293 K is AG'º = +15 kJ mol-1. If you had a solution, at pH = 7.0 and T = 293 K, containing this protein: a) What fraction of Hisa residues are protonated? b) What fraction of Hisg residues are protonated? c) What is the pK, of Hisg?
Let's consider a protein with two surface-exposed histidine residues: • Hisa is a "typical" histidine residue with pK = 6.2 • Hisg is involved in a stabilizing interaction (His-NH* --- -0,C-Glu) with a neighboring glutamic acid residue. For Hisg, the Gibbs free energy of deprotonation at pH = 7.0 and T = 293 K is AG'º = +15 kJ mol-1. If you had a solution, at pH = 7.0 and T = 293 K, containing this protein: a) What fraction of Hisa residues are protonated? b) What fraction of Hisg residues are protonated? c) What is the pK, of Hisg?
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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
Transcribed Image Text:Let's consider a protein with two surface-exposed histidine residues:
• Hisa is a "typical" histidine residue with pKa = 6.2
Hisg is involved in a stabilizing interaction (His-NH* --- -02C-Glu) with a
neighboring glutamic acid residue. For Hisg, the Gibbs free energy of
deprotonation at pH = 7.0 and T = 293 K is AG'° = +15 kJ mol-1.
If you had a solution, at pH = 7.0 and T = 293 K, containing this protein:
a) What fraction of Hisa residues are protonated?
b) What fraction of Hisg residues are protonated?
c) What is the pK, of Hisg?
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