The 20 common amino acids

Name Formula (note 1) Three- letter code Single-letter code Occurrence in proteins (%) (note 2) Properties
Glycine Gly G 7.2 small, flexible, nonpolar
Alanine Ala A 7.8 small, hydrophobic, nonpolar
Serine Ser S 6.8 small, hydrophilic, hydrogen-bonding
Threonine Thr T 5.9 hydrophilic, hydrogen-bonding
Proline Pro P 5.2 hydrophobic, rigid
Valine Val V 6.6 hydrophobic
Leucine Leu L 9.1 large, hydrophobic
Isoleucine Ile I 5.3 large, hydrophobic
Methionine Met M 2.3 large, hydrophobic, pot. metal binder (Fe, Zn,...)
Cysteine Cys C 1.9 hydrophobic, forms disulfide bridges, pot. metal binder (Zn, Fe,...)
Aspartic acid (Aspartate) Asp D


5.3 hydrophilic, acidic, negative charge, pot. metal binder (Ca, Mg,...)
Glutamic acid (Glutamate) Glu E


6.3 large, hydrophilic, acidic, negative charge, pot. metal binder (Ca, Mg,...)
Asparagine Asn N


4.3 hydrophilic, polar, hydrogen bonding
Glutamine Gln Q


4.2 large, hydrophilic, polar, hydrogen bonding
Arginine Arg R


5.1 large, hydrophilic, basic, positive charge
Lysine Lys K


5.9 large, hydrophilic, basic, positive charge
Histidine His H 2.3 hydrophilic, intermediate pKa, proton shuttle, pot. metal binder (Fe, Zn,...)
Phenylalanine Phe F


3.9 large, hydrophobic
Tyrosine Tyr Y


3.2 large, hydrophobic, hydrogen bonding, slightly acidic
Tryptophan Trp W

"two rings"

1.4 large, hydrophobic, hydrogen bonding


  1. The formula images are taken from the LIGAND database in KEGG.
  2. Values from R.F. Doolittle (1989), calculated from 1150 protein sequences.

Copyright © 2001 Per Kraulis $Date: 2001/01/19 13:18:15 $