Amino Acids - one-letter codes

One-letter amino acid codes

The Code Symbols
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The symbols are listed, in alphabetical order of amino-acid names, in Table 1. Table 5 gives them in alphabetical order of symbols.
 

Table 5. The One-Letter Symbols

One-letter symbol	Three-letter symbol	Amino acid
A	Ala	alanine
B	Asx	aspartic acid or asparagine
C	Cys	cysteine
D	Asp	aspartic acid
E	Glu	glutamic acid
F	Phe	phenylalanine
G	Gly	glycine
H	His	histidine
I	Ile	isoleucine
K	Lys	lysine
L	Leu	leucine
M	Met	methionine
N	Asn	asparagine
P	Pro	proline
Q	Gln	glutamine
R	Arg	arginine
S	Ser	serine
T	Thr	threonine
U*	Sec	selenocysteine
V	Val	valine
W	Trp	tryptophan
X**	Xaa	unknown or 'other' amino acid
Y	Tyr	tyrosine
Z	Glx	glutamic acid or glutamine (or substances such as 4-carboxyglutamic acid and 5-oxoproline that yield glutamic acid on acid hydrolysis of peptides)

 * See JCBN/NC-IUBMB Newsletter 1999 for recommendations on selenocysteine
** See the Addendum for an alternative use of X.

Source: http://www.chem.qmul.ac.uk/iupac/AminoAcid/A2021.html#AA211