Definition of Amino acid symbols

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Amino acid symbols: Symbols that stand for the amino acids, the building blocks of protein. Each amino acid has both a three-letter symbol and a single-letter symbol. For example, the three-letter and single-letter symbols for alanine are Ala and A. The three-letter symbols (such as Ala) are much more widely used than the single letter ones (such as A).

Therefore, the following list is limited to the three-letter symbols and is further limited to those 20 alpha-amino acids specified by the genetic code:

• Alanine: Ala
• Arginine: Arg
• Asparagine: Asn
• Aspartic acid: Asp
• Cysteine: Cys
• Glutamic acid: Glu
• Glutamine: Gln
• Glycine: Gly
• Histidine: His
• Isoleucine: Ile
• Leucine: Leu
• Lysine: Lys
• Methionine: Met
• Phenylalanine: Phe
• Proline: Pro
• Serine: Ser
• Threonine: Thr
• Tryptophan: Trp
• Tyrosine: Tyr
• Valine: Val

These three-letter symbols for amino acids are used not only to refer to an individual amino acid but also to present the amino acid sequence of a polypeptide or a protein. For example, part of the sequence of insulin reads: Gly-Ile-Val-Glu-Gln-Cys-Cys-Ala-Ser-Val. The N-terminal residue of the polypeptide or protein is by convention always on the left and the sequence reads from left-to-right toward the C-terminal residue of the polypeptide or protein.