Biochemistry 2280A Study Guide - Final Guide: Aspartic Acid, Beta Sheet, Histidine
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4 Jan 2017
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Consider the peptide:
NH2-GAPAGPAGTGKTETTKDLAKSMALLCWFNCS-COOH
Table I. pK values of some amino acids
amino acid | pK of side chain or terminal group |
---|---|
Alanine (Ala or A) | uncharged |
Arginine (Arg or R) | 12.5 |
Asparagine (Asn or N) | uncharged |
Aspartic acid (Asp or D) | 3.9 |
Cysteine (Cys or C) | 8.3 |
Glutamic acid (Glu or E) | 4.3 |
Glycine (Gly or G) | uncharged |
Histidine (His or H) | 6.0 |
Leucine (Leu or L) | uncharged |
Lysine (Lys or K) | 10.8 |
Phenylalanine (Phe or F) | uncharged |
Serine (Ser or S) | uncharged |
Tryptophan (Trp or W) | uncharged |
Tyrosine (Tyr or Y) | 10.9 |
Valine (Val or V) | uncharged |
peptide N terminus | 7.8 |
peptide C terminus | 3.6 |
Using Table I above, determine the net charge of the peptide at pH9.
(the answer is not -1 or 1)
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=?
------------------------------------------------------------------------------------------------------------------------------------------------------
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 |