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Table of pKa and pI values

Amino acid pKa1  pKa2 pKa3    pI
Glycine 2.34  9.60   ---   5.97
Alanine 2.34  9.69   ---   6.00
Valine 2.32  9.62   ---   5.96
Leucine 2.36  9.60   ---   5.98
Isoleucine 2.36  9.60   ---   6.02
Methionine 2.28  9.21   ---   5.74
Proline 1.99 10.60   ---   6.30
Phenylalanine 1.83  9.13   ---   5.48
Tryptophan 2.83  9.39   ---   5.89
Asparagine 2.02  8.80   ---   5.41
Glutamine 2.17  9.13   ---   5.65
Serine 2.21  9.15   ---   5.68
Threonine 2.09  9.10   ---   5.60
Tyrosine 2.20  9.11   ---   5.66
Cysteine 1.96  8.18   ---   5.07
Aspartic acid 1.88  9.60   3.65   2.77
Glutamic acid 2.19  9.67   4.25   3.22
Lysine 2.18  8.95 10.53   9.74
Arginine 2.17  9.04 12.48 10.76
Histidine 1.82  9.17   6.00   7.59
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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary