Download Amino Acid One and Three Letter Codes - MBios 303

Amino Acid One and Three Letter Codes
As you know, some of the amino acid one- and three-letter abbreviations are not necessarily what you
may expect them to be. I wanted to post a description of how these names were decided upon in case it
helps you study.
This information was taken from: Branden and Tooze, Introduction to Protein Structure, 2nd ed. Garland
Publishing, New York, NY. 1999. (It takes a lot of work to put together a book, paper, etc. – make sure
you give credit where credit is due. Always reference anything you take from another source!)
There are some easy ways of remembering the one-letter code for amino acids. If only one amino acid
begins with a certain letter, that letter is used:
C = Cys = Cysteine
H = His = Histidine
I = Ile = Isoleucine
M = Met = Methionine
S = Ser = Serine
V = Val = Valine
If more than one amino acid begins with a certain letter, that letter is assigned to the most commonly
occurring amino acid:
A = Ala = Alanine
G = Gly = Glycine
L = Leu = Leucine
P = Pro = Proline
T = Thr = Threonine
Some of the others are phonetically suggestive:
F = Phe = Phenylalanine (“Fenylalanine”)
R = Arg = Arginine (“aRginine”)
Y = Tyr = Tyrosine (“tYrosine”)
W = Trp = Tryptophan (double ring in the molecule)
In other cases a letter close to the initial is used. Amides have letters from the middle of the alphabet.
The smaller molecules (D, N, B) are earlier in the alphabet than the larger ones (E, Q, Z).
D = Asp = Aspartic Acid (near A)
N = Asn = Asparagine (contains N)
E = Glu = Glutamic acid (near G)
Q = Gln = Glutamine (“Q-tamine”)
K= Lys = Lysine (near L)