Amino acid pKa and pKi values

The proteinogenic amino acids are amphoteric and have two or three pK values, depending on their side chains.  pKa1 is the α-carboxyl group, pKa2 is the α-ammonium ion, pKa3 is the side chain group if applicable and pI is the isoelectric point at which the amino acid has no net charge.  At a pH lower than pI the amino acid is positively charged, at higher pH than pI the amino acid is negatively charged.

Amino acids with neutral side chains

Amino acid                       Code                        pKa1                       pKa2                            pKa3                                 pI


Glycine G2.34 9.60 -5.97

Alanine A2,34 9.69  -6.00

Valine V2.32 9.62  -5.96

Leucine L2.36 9.60  -5.98

Isoleucine I2.36 9.60  -6.02

Methionine M2.28 9.21  -5.74

Proline P1.99 10.60  -6.30

Phenylalanine F1.83 9.13  -5.48

Tryptophan W2.83 9.39  -5.89

Asparagine N2.02 8.80  -5.41

Glutamine Q2.179.13 -5.65

Serine S2.219.15 -5.68

Threonine T2.099.10 -5.60

Tyrosine Y2.209.11 -5.66

Amino acids with ionisable side chains

Amino acid                    Code                           pKa1                      pKa2                         pKa3                               pI


Cysteine  C 1.96 10.28 8.18 5.07

Aspartic acid  D 1.88 9.60 3.65 2.77

Glutamic acid  E 2.19 9.67 4.25 3.22

Lysine  K 2.18 8.95 10.53 9.74

Arginine  R 2.17 9.04 12.48 10.76

Histidine  H 1.82 9.17 6.00 7.59


Data from: Carey and Giuliano (2011) Amino acids, peptides and proteins. Organic Chemistry 8 th Edition, 25, 1126 McGraw Hill, ISBN-13: 978-0077354770



Learn more

Contact Information

To place an order, or for customer services, order processing or technical support please contact us on:

UK, Europe and RoW
Tel: (+44) 01392 422205
Fax: (+44) 01392 279510
[email protected]

USA and Canada

Tel: 610-994-1134

Toll Free: 855-FOCUS21 (855-362-8721)

Fax: 610-465-9100

[email protected] 


France

CliniSciences
Tel : +33 9 77 40 09 09
Fax :  +33 9 77 40 10 11
Orders and customer support : [email protected]


Germany, Switzerland, Austria

BIOZOL Diagnostics 

Tel: +49 (089) 3799 666-6

Fax: +49 (089) 3799 666-99
Orders, Technical and Customer support: [email protected]


Italy
Labospace
Tel: +39 02 35980841
Fax +39 02 359808004
Orders: [email protected]


Spain and Portugal
Abyntek Biopharma
Tel: +34 94 404 80 80

Fax: +34 94 404 80 81
Orders: [email protected]


China

BIOHUB INTERNATIONAL 

上海起发实验试剂有限公司

Tel: +86-15921799099

Tel: +86-021-50724187

Fax: +86-021-50724961

Orders: [email protected]

India
Biotechno Labs
Tel: +91-8860924629
07291852429
Orders, Technical and Customer support: [email protected]


Japan

Namiki Shoji Co.
Tel:+81-050-5527-9850
Fax:+81-3-3352-2196
email: [email protected]


All distributors >