3. The trp repressor is a homodimer with 107 amino acid residues per monomer. The content of proton dissociable groups of each monomer is given below: Side chain pKa number/monomer ZpH 4 ZpH 6 Arginine Aspartate Glutamate Histidine 12.5 4.0 4.0 9. 10 6.0 10.0 Lysine Tyrosine -NH3® —СООН 9.5 2 7.0 4.0 1 1 (a) (' : ) The isoelectric point (pl) of the protein, i.e., the pH at which the overall electrostatic charge on the protein E z = 0, is 5.3. Although the pKa values in the table above are only approximate values generally characteristic of residues with unhindered exposure to solvent, confirm that the overall charge on the protein must pass through zero between pH 4 and pH 6.

Biochemistry
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Chapter1: Biochemistry: An Evolving Science
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3. The trp repressor is a homodimer with 107 amino acid residues per monomer. The content of proton
dissociable groups of each monomer is given below:
Side chain
pKa
number/monomer
ZpH 4
ZpH 6
12.5
Arginine
Aspartate
Glutamate
9.
4.0
4.0
10
Histidine
6.0
2
Lysine
Tyrosine
-NH3®
10.0
6
9.5
2
7.0
1
-СООН
4.0
1
(a) ( : ) The isoelectric point (pl) of the protein, i.e., the pH at which the overall electrostatic charge
on the protein E z = 0, is 5.3. Although the pKa values in the table above are only approximate values
generally characteristic of residues with unhindered exposure to solvent, confirm that the overall charge
on the protein must pass through zero between pH 4 and pH 6.
) Estimate what must be the average pKa value of all of the residues containing carboxylic
(b) (
acid groups using the H-H equation below, assuming that the pka values of the positively charged
groups do not change from the values given in the table above:
pH
pKa
log [base]/[acid]
+
DNA te
Transcribed Image Text:3. The trp repressor is a homodimer with 107 amino acid residues per monomer. The content of proton dissociable groups of each monomer is given below: Side chain pKa number/monomer ZpH 4 ZpH 6 12.5 Arginine Aspartate Glutamate 9. 4.0 4.0 10 Histidine 6.0 2 Lysine Tyrosine -NH3® 10.0 6 9.5 2 7.0 1 -СООН 4.0 1 (a) ( : ) The isoelectric point (pl) of the protein, i.e., the pH at which the overall electrostatic charge on the protein E z = 0, is 5.3. Although the pKa values in the table above are only approximate values generally characteristic of residues with unhindered exposure to solvent, confirm that the overall charge on the protein must pass through zero between pH 4 and pH 6. ) Estimate what must be the average pKa value of all of the residues containing carboxylic (b) ( acid groups using the H-H equation below, assuming that the pka values of the positively charged groups do not change from the values given in the table above: pH pKa log [base]/[acid] + DNA te
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