Polish version
Lukasz P. Kozlowski, PhD
Poland, 2013
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Calculation of protein isoelectric point

Welcome, here is the place were you can online estimate protein isoelectric point. It is higly important to know this parametr, even approximately, during molecular biology analyses, especially in 2D gel electrophoresis and isoelectric focusing. Additionally, there was presented short protein isoelectric point calculation manual. You can learn how to write a computer program which will estimate isoelectric point or simply download ready one. Presented C++ program make use of bisection method, one of the most widely used numerical algorithms.

Below is the text area where you can paste one, raw amino acid sequence of analyzed protein (peptide).

Note: the sequence should be in UPPERCASE LETTERS (lowercase letters and meaningless uppercase leters will be ignored)

Input example
If you would like to analyze Ala-Pro-Lys-His-Ala-Tyr peptide, please enter APKHAY

Additionally, you can choose between eight different sets of pK values (for more information see a table).

If you are interested in calculating isoelectric point and molecular weight for any known proteins from PDB or SwissProt database, you can find them in prepared files (see links below).

Theoretical basis of isoelectric point calculation, i.e. how to calculate protein isoelectric point using Henderson-Hasselbach equation

Practical point of view (examplary program, which can calculate isoelectric point of given protein)

Free QT4 version of Isoelectric Point Calculator v. 1.0  with GUI  

PDB and SwissProt databases with precalculated molecular weight and isoelectric points    New!!!

Links to other online isoelectric point estimation tools


This site was cited > 100 times (according Google Scholar)

Partial list of recent publications and patents citing isoelectric.ovh.org:

  1. Niwa T, Ying BW, Saito K, Jin W, Takada S, Ueda T, Taguchi H. Bimodal protein solubility distribution revealed by an aggregation analysis of the entire ensemble of Escherichia coli proteins. Proc Natl Acad Sci U S A. 2009 Mar 17;106(11):4201-6. Epub 2009 Feb 27. PubMed PMID: 19251648; PubMed Central PMCID: PMC2657415.
  2. Muller SA, Kohajda T, Findeiss S, Stadler PF, Washietl S, Kellis M, von Bergen M, Kalkhof S. Optimization of parameters for coverage of low molecular weight proteins. Anal Bioanal Chem. 2010 Dec;398(7-8):2867-81. Epub 2010 Aug 28. PubMed  PMID: 20803007; PubMed Central PMCID: PMC2990009.
  3. Tiengo A, Barbarini N, Troiani S, Rusconi L, Magni P. A Perl procedure for protein identification by Peptide Mass Fingerprinting. BMC Bioinformatics. 2009 Oct 15;10 Suppl 12:S11. PubMed PMID: 19828071; PubMed Central PMCID: PMC2762060
  4. Bao Y, Wang Q, Liu H, Lin Z. A small HSP gene of bloody clam (Tegillarca granosa) involved in the immune response against Vibrio parahaemolyticus and lipopolysaccharide. Fish Shellfish Immunol. 2011 Feb;30(2):729-33. Epub 2010 Dec 21. PubMed PMID: 21172441.
  5. Siegel SJ, Percopo CM, Dyer KD, Zhao W, Roth VL, Mercer JM, Rosenberg HF. RNase 1 genes from the family Sciuridae define a novel rodent ribonuclease cluster. Mamm Genome. 2009 Nov-Dec;20(11-12):749-57. Epub 2009 Sep 22. PubMed PMID: 19771477; PubMed Central PMCID: PMC2809794.
  6. Uskokovic V, Castiglione Z, Cubas P, Zhu L, Li W, Habelitz S. Zeta-potential and particle size analysis of human amelogenins. J Dent Res. 2010 Feb;89(2):149-53. Epub 2009 Dec 29. PubMed PMID: 20040742.
  7. Tamburro D, Fredolini C, Espina V, Douglas TA, Ranganathan A, Ilag L, Zhou W,  Russo P, Espina BH, Muto G, Petricoin EF 3rd, Liotta LA, Luchini A. Multifunctional core-shell nanoparticles: discovery of previously invisible biomarkers. J Am Chem Soc. 2011 Nov 30;133(47):19178-88. Epub 2011 Nov 3. PubMed PMID: 21999289; PubMed Central PMCID: PMC3223427.
  8. Krenn BM, Egorov A, Romanovskaya-Romanko E, Wolschek M, Nakowitsch S, Ruthsatz T, Kiefmann B, Morokutti A, Humer J, Geiler J, Cinatl J, Michaelis M, Wressnigg N, Sturlan S, Ferko B, Batishchev OV, Indenbom AV, Zhu R, Kastner M, Hinterdorfer P, Kiselev O, Muster T, Romanova J. Single HA2 mutation increases the infectivity and immunogenicity of a live attenuated H5N1 intranasal influenza vaccine candidate lacking NS1. PLoS One. 2011 Apr 7;6(4):e18577. PubMed PMID: 21490925; PubMed Central PMCID: PMC3072404.
  9. Tao F, Fan M, Zhao W, Lin Q, Ma R. A novel cationic ribonuclease with antimicrobial activity from Rana dybowskii. Biochem Genet. 2011 Jun;49(5-6):369-84. Epub 2011 Jan 23. PubMed PMID: 21259045.
  10. Jang IK, Pang Z, Yu J, Kim SK, Seo HC, Cho YR. Selectively enhanced expression of prophenoloxidase activating enzyme 1 (PPAE1) at a bacteria clearance site in the white shrimp, Litopenaeus vannamei. BMC Immunol. 2011 Dec 30;12:70. PubMed PMID: 22208405; PubMed Central PMCID: PMC3268739.
  11. PATENT: XOMA TECHNOLOGY LTD. (Berkeley, California, 94710, US) EVANS, Mark Christopher (2910 Seventh StreetBerkeley, California, 94710, US) STUDNICKA, Gary (2910 Seventh StreetBerkeley, California, 94710, US)