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. 2020 Jun 17;9(6):330. doi: 10.3390/antibiotics9060330

Table 2.

Enlists all 20 proteogenic amino acids. It highlights acidic, basic and neutral amino acids with their pKa and pI values. Data collected from Haynes, William M., 2014 [159].

Name Acidic Basic Neutral pKa1 (α-Carboxyl Group) PKa2 (α-Amino Group) pKa3 (Side Chain) pI (Isoelectronic Point)
Alanine 2.34 9.69 6.00
Arginine 2.17 9.04 12.48 10.76
Asparagine 2.02 8.80 5.41
Aspartic acid 1.88 9.60 3.65 2.77
Cysteine 1.96 10.28 8.18 5.07
Glutamic acid 2.19 9.67 4.25 3.22
Glutamine 2.17 9.13 5.65
Glycine 2.34 9.60 5.97
Histidine 1.82 9.17 6.00 7.95
Isoleucine 2.36 9.60 6.02
Leucine 2.36 9.60 5.98
Lysine 2.18 8.95 10.53 9.74
Methionine 2.28 9.21 5.74
Phenylalanine 1.83 9.13 5.48
Proline 1.99 10.60 6.30
Serine 2.21 9.15 5.68
Threonine 2.09 9.10 5.60
Tryptophan 2.83 9.39 5.89
Tyrosine 2.20 9.11 10.07 5.66
Valine 2.32 9.62 5.96