Nomenclature and Symbolism for Amino Acids and Peptides

Table 1. α-Amino acids incorporated into protein under mRNA direction.

This version of Table 1 does not use the HTML table format. In order to simulate a table layout subscripts are not used.

The systematic names and formulas given refer to hypothetical forms in which amino groups are unprotonated and carboxyl groups are undissociated. This convention is useful to avoid various nomenclatural problems but should not be taken to imply that these structures represent an appreciable fraction of the amino-acid molecules.

 Trivial       Symbols  Systematic name (Note c)       Formula (Note g)
 name (Note a) (Note b) 
 Alanine        Ala  A  2-Aminopropanoic acid          CH3-CH(NH2)-COOH 

 Arginine       Arg  R  2-Amino-5-guanidinopentanoic   H2N-C(=NH)-NH-[CH2]3-CH(NH2)-COOH 
 Asparagine     Asn  N  2-Amino-3-carbamoylpropanoic   H2N-CO-CH2-CH(NH2)-COOH 
               (Note d)     acid
 Aspartic acid  Asp  D  2-Aminobutanedioic acid        HOOC-CH2-CH(NH2)-COOH
               (Note d)
 Cysteine       Cys  C  2-Amino-3-mercaptopropanoic    HS-CH2-CH(NH2)-COOH 
 Glutamine      Gln  Q  2-Amino-4-carbamoylbutanoic    H2N-CO-[CH2]2-CH(NH2)-COOH 
               (Note d)     acid
 Glutamic acid  Glu  E  2-Aminopentanedioic acid       HOOC-[CH2]2-CH(NH2)-COOH 
               (Note d)
 Glycine        Gly  G  Aminoethanoic acid             CH2(NH2)-COOH 
 Histidine      His  H  2-Amino-3-(1H-imidazol-4-yl)-
                            propanoic acid             
 Isoleucine     Ile  I  2-Amino-3-methylpentanoic      C2H5-CH(CH3)-CH(NH2)-COOH 
                            acid (Note e)  
 Leucine        Leu  L  2-Amino-4-methylpentanoic      (CH3)2CH-CH2-CH(NH2)-COOH 
 Lysine         Lys  K  2,6-Diaminohexanoic acid       H2N-[CH2]4-CH(NH2)-COOH 
 Methionine     Met  M  2-Amino-4-(methylthio)butanoic CH3-S-[CH2]2-CH(NH2)-COOH 
acid Phenylalanine Phe F 2-Amino-3-phenylpropanoic C6H5-CH2-CH(NH2)-COOH acid Proline Pro P Pyrrolidine-2-carboxylic acid
 Serine         Ser  S  2-Amino-3-hydroxypropanoic     HO-CH2-CH(NH2)-COOH 
 Threonine      Thr  T  2-Amino-3-hydroxybutanoic      CH3-CH(OH)-CH(NH2)-COOH 
                            acid (Note e) 
 Tryptophan     Trp  W  2-Amino-3-(lH-indol-3-yl)-
                            propanoic acid             
 Tyrosine       Tyr  Y  2-Amino-3-(4-hydroxyphenyl)-
                            propanoic acid             
 Valine         Val  V  2-Amino-3-methylbutanoic       (CH3)2CH-CH(NH2)-COOH 
 Unspecified    Xaa  X 
 amino acid    (Note f)

a The trivial name refers to the L or D or 
DL-amino acid; for those that are chiral only the L-amino acid is used for protein biosynthesis.

b Use of the one-letter symbols should be restricted to the comparison of long sequences (3AA-20).

c The fully systematic forms ethanoic, propanoic, butanoic and pentanoic may alternatively be called acetic, propionic, butyric and valeric, respectively. Similarly, butanedioic = succinic, 3-carbamoylpropanoic = succinamic, pentanedioic = glutaric, and 4-carbamoylbutanoic = glutaramic.

d The symbol Asx denotes Asp or Asn; likewise B denotes N or D. Glx and Z likewise represent glutamic acid or glutamine or a substance, such as 4-carboxyglutamic acid, Gla (3AA-15.2.6), or 5-oxoproline, Glp (3AA-16.5), that yields glutamic acid on acid hydrolysis of peptides.

e See 3AA-3 and -4 for stereochemical designation.

f See Addendum for alternative use of X.

g All numbers should be subscripts in the Formula column. Where a graphic formula is used this may appear on the left on the next line.

Return to 3AA-1.