HNF 150 Study Guide - Midterm Guide: Nitrogen Balance, Amine, Blood Proteins
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Using the information in the table below, enter the correct pH that should be used to separate the following three amino acids by electrophoresis:
(a) Glu, Lys, and Thr: pH=?
(b) His, Lys, and Arg: pH=?
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Amino Acid | pKa of α-COOH | pKa of α-NH3+ | pKa of Side Chain | Isoelectric Point (pI) |
---|---|---|---|---|
Alanine | 2.35 | 9.87 | - | 6.11 |
Arginine | 2.01 | 9.04 | 12.48 | 10.76 |
Asparagine | 2.02 | 8.80 | - | 5.41 |
Aspartic acid | 2.10 | 9.82 | 3.86 | 2.98 |
Cysteine | 2.05 | 10.25 | 8.00 | 5.02 |
Glutamic acid | 2.10 | 9.47 | 4.07 | 3.08 |
Glutamine | 2.17 | 9.13 | - | 5.65 |
Glycine | 2.35 | 9.78 | - | 6.06 |
Histidine | 1.77 | 9.18 | 6.10 | 7.64 |
Isoleucine | 2.32 | 9.76 | - | 6.04 |
Leucine | 2.33 | 9.74 | - | 6.04 |
Lysine | 2.18 | 8.95 | 10.53 | 9.74 |
Methionine | 2.28 | 9.21 | - | 5.74 |
Phenylalanine | 2.58 | 9.24 | - | 5.91 |
Proline | 2.00 | 10.60 | - | 6.30 |
Serine | 2.21 | 9.15 | - | 5.68 |
Threonine | 2.09 | 9.10 | - | 5.60 |
Tryptophan | 2.38 | 9.39 | - | 5.88 |
Tyrosine | 2.20 | 9.11 | 10.07 | 5.63 |
Valine | 2.29 | 9.72 | - | 6.00 |
Amino Acid | M.W. g/mol | pKa for side chain |
Alanine | 89.1 | |
Arginine | 174.2 | 12.48 |
Asparagine | 132.1 | |
Aspartate | 133.1 | 3.90 |
Cysteine | 121.1 | 8.37 |
Glycine | 75.0 | |
Glutamate | 147.1 | 4.07 |
Glutamine | 146.1 | |
Histidine | 155.1 | 6.04 |
Isoleucine | 131.2 | |
Leucine | 131.2 | |
Lysine | 146.2 | 10.54 |
Methionine | 149.2 | |
Proline | 115.1 | |
Phenylalanine | 165.2 | |
Serine | 105.1 | |
Threonine | 119.1 | |
Tryptophan | 204.2 | |
Tyrosine | 181.2 | 10.46 |
Valine | 117.1 |
Take a look at your pKa table for the amino acids. It turns out that when these side chains are in a protein, they can have very different pKa values. Explain the following observations:
a. In the enzyme medium chain acyl-CoA dehydrogenase (b-oxidation of fatty acids), E376 has a measured pKa ~ 8.0. It is found in a very hydrophobic environment. What could account for it elevated pKa?
b. For the enzyme aconitase (Krebbâs Cycle), a catalytic serine is known to have a pKa ~ 8. What kind of factors could account for this decrease in pKa?