Abbreviations and symbols for commonly occurring amino acids

Each amino acid name has an associated three-letter abbreviation and a oneletter symbol (Fig.1 ). The one-letter codes are determined by the following rules.

Figure 1. Abbreviations and symbols for the standard amino acids.
1. Unique first letter: If only one amino acid begins with a given letter, then that letter is used as its symbol. For example, V = valine.
2. Most commonly occurring amino acids have priority: If more than one amino acid begins with a particular letter, the most common of these amino acids receives this letter as its symbol. For example, glycine is more common than glutamate, so G = glycine.
3. Similar sounding names: Some one-letter symbols sound like the amino acid they represent. For example, F = phenylalanine, or W = tryptophan (“twyptophan” as Elmer Fudd would say).
4. Letter close to initial letter: For the remaining amino acids, a one-letter symbol is assigned that is as close in the alphabet as possible to the initial letter of the amino acid, for example, K = lysine. Furthermore, B is assigned to Asx, signifying either aspartic acid or asparagine; Z is assigned to Glx, signifying either glutamic acid or glutamine; and X is assigned to an unidentified amino acid.