Table 3.2: pKa values of acidic and basic constituents of free amino acids at 25°C
Amino acid PKa value Carboxyl group Amino group Side chain
Glycine 2.4 2.4 - -
Alanine 9.8 2.3 - -
Valine 2.3 - - -
Leucine 2.3 - - -
Isoleucine 2.3 - - -
Methionine 2.1 - - -
Proline 2.0 - - -
Phenylalanine 2.2 - - -
Tryptophan 2.5 - - -
Serine 2.2 - - -
Threonine 2.1 - - -
Cysteine 1.9 - - -
Tyrosine 2.2 - - -
Asparagine 2.1 - - -
Glutamine 2.2 - - -
Aspartic acid 2.0 - - -
Glutamic acid 2.1 - - -
Lysine 2.2 - - -
Arginine 1.8 - - -
Histidine 1.8 - - -