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?
Proteins
We generally tend to think of proteins only from a dietary lens, as a component of what we eat. However, they are among the most important and abundant organic macromolecules in the human body, with diverse structures and functions. Every cell contains thousands and thousands of proteins, each with specific functions. Some help in the formation of cellular membrane or walls, some help the cell to move, others act as messages or signals and flow seamlessly from one cell to another, carrying information.
Protein Expression
The method by which living organisms synthesize proteins and further modify and regulate them is called protein expression. Protein expression plays a significant role in several types of research and is highly utilized in molecular biology, biochemistry, and protein research laboratories.
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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The expresion ytou have like [deprotonate][protonate]. Are they multiplying or dividing? Is not clear. Could you clarifiy that?
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