Consider a protein with two surface-exposed histidine residues: HisA is a “typical” histidine residue with a pKa = 6.2 HisB 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?
Consider a protein with two surface-exposed histidine residues: HisA is a “typical” histidine residue with a pKa = 6.2 HisB 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?
Biochemistry
6th Edition
ISBN:9781305577206
Author:Reginald H. Garrett, Charles M. Grisham
Publisher:Reginald H. Garrett, Charles M. Grisham
Chapter26: Synthesis And Degradation Of Nucleotides
Section: Chapter Questions
Problem 22P
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Consider a protein with two surface-exposed histidine residues:
- HisA is a “typical” histidine residue with a pKa = 6.2
- HisB 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?
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