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Table 4 Most commonly used pKa values for the ionizable groups of proteins. Note that Bjellqvist and ProMoST use different amounts of additional pKa values (not shown), which take into account the relative position of the ionized group (whether it is located on the N- or C- terminus or in the middle). For more details, see References 4 and 5 and the “Theory” section on the IPC web site

From: IPC – Isoelectric Point Calculator

Amino acid NH2 COOH C D E H K R Y
EMBOSS [29] 8.6 3.6 8.5 3.9 4.1 6.5 10.8 12.5 10.1
DTASelect [30] 8 3.1 8.5 4.4 4.4 6.5 10 12 10
Solomons [31] 9.6 2.4 8.3 3.9 4.3 6 10.5 12.5 10.1
Sillero [32] 8.2 3.2 9 4 4.5 6.4 10.4 12 10
Rodwell [33] 8 3.1 8.33 3.68 4.25 6 11.5 11.5 10.07
Patrickios [34] 11.2 4.2 - 4.2 4.2 - 11.2 11.2 -
Wikipedia 8.2 3.65 8.18 3.9 4.07 6.04 10.54 12.48 10.46
Lehninger [35] 9.69 2.34 8.33 3.86 4.25 6 10.5 12.4 10
Grimsley [15] 7.7 3.3 6.8 3.5 4.2 6.6 10.5 12.04a 10.3
Toseland [36] 8.71 3.19 6.87 3.6 4.29 6.33 10.45 12 9.61
Thurlkill [37] 8 3.67 8.55 3.67 4.25 6.54 10.4 12 9.84
Nozaki [38] 7.5 3.8 9.5 4 4.4 6.3 10.4 12 9.6
Dawson [39] 8.2b 3.2b 8.3 3.9 4.3 6 10.5 12 10.1
Bjellqvist [16] 7.5 3.55 9 4.05 4.45 5.98 10 12 10
ProMoST [17] 7.26 3.57 8.28 4.07 4.45 6.08 9.8 12.5 9.84
IPC_protein 9.094 2.869 7.555 3.872 4.412 5.637 9.052 11.84 10.85
IPC_peptide 9.564 2.383 8.297 3.887 4.317 6.018 10.517 12.503 10.071
  1. aArg was not included in the study, and the average pKa from all other pKa sets was taken
  2. bNH2 and COOH were not included in the study, and they were arbitrary taken from Sillero set