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| Type | Name | Code (3) | Code (1) | pK1 | pK2 | pKR | Mr | Hydro-* |
|---|---|---|---|---|---|---|---|---|
| Non-polar | Alanine | Ala | A | 2.3 | 9.9 | 89 | 0.616 | |
| Charged (+) | Arginine | Arg | R | 1.8 | 9 | 12.5 | 174 | 0 |
| Polar-neutral | Asparagine | Asn | N | 2.1 | 8.8 | 132 | 0.236 | |
| Charged (-) | Aspartate | Asp | D | 2 | 10 | 3.9 | 133 | 0.028 |
| Polar-neutral | Cysteine | Cys | C | 1.9 | 10.8 | 8.3 | 121 | 0.68 |
| Charged (-) | Glutamate | Glu | E | 2.2 | 9.7 | 4.3 | 147 | 0.043 |
| Polar-neutral | Glutamine | Gln | Q | 2.2 | 9.1 | 146 | 0.251 | |
| Non-polar | Glycine | Gly | G | 2.4 | 9.8 | 75 | 0.501 | |
| Charged (+) | Histidine | His | H | 1.8 | 9.2 | 6 | 155 | 0.165 |
| Non-polar | Isoleucine | Ile | I | 2.3 | 9.8 | 131 | 0.943 | |
| Non-polar | Leucine | Leu | L | 2.3 | 9.7 | 131 | 0.943 | |
| Charged (+) | Lysine | Lys | K | 2.2 | 9.2 | 10.8 | 146 | 0.283 |
| Non-polar | Methionine | Met | M | 2.1 | 9.3 | 149 | 0.738 | |
| Aromatic | Phenylalanine | Phe | F | 1.8 | 9.1 | 165 | 1 | |
| Non-polar | Proline | Pro | P | 2 | 10.6 | 115 | 0.711 | |
| Polar-neutral | Serine | Ser | S | 2.1 | 9.2 | 105 | 0.359 | |
| Polar-neutral | Threonine | Thr | T | 2.1 | 9.1 | 119 | 0.45 | |
| Aromatic | Tryptophan | Trp | W | 2.4 | 9.4 | 204 | 0.878 | |
| Aromatic | Tyrosine | Tyr | Y | 2.2 | 9.1 | 10.9 | 181 | 0.88 |
| Non-polar | Valine | Val | V | 2.3 | 9.6 | 117 | 0.825 |
Abbreviations and Definitions:
Mr: Relative molecular mass. Also measured in units of dalton (Da). One Da is one twelfth of the mass of the nuclide 12C.
pK1: The pK of the carboxyl group of the amino acid.
pK2: The pK of the amino group of the amino acid.
pKR: The pK of the side arm R of the amino acid. Only the specified AA's have ionizable side chains.
Reference for hydrophobicity values: Black, S.D. and Mould, D.R. (1991) Anal. Biochem. 193, 72-82.
The melting points of amino acids are in the range of 200-300°C. The melting points cannot be determined accurately as the heating of the amino acids leads to their decomposition before the melting process. The zwitterion nature of amino acids, with both positive and negative charges on the same molecule, allows tight binding of amino acids to one another by ionic interactions. Hence the breaking of these inter-molecular interactions require relatively high energy leading to high melting points.