By Contributor
Updated Mar 24, 2022
The isoelectric point (pI) is the pH at which a protein carries no net charge. It is a fundamental property in biochemistry, influencing solubility, stability, and interaction with other molecules. Because the pI depends on a protein’s amino‑acid composition, you need the exact sequence to calculate it.
If you already have the sequence, skip to Step 8. Otherwise, retrieve it from the UniProt database.
Enter the protein name or keyword in the search box and click Search.
Browse the results, select the correct entry, and record its accession number.
Navigate to the ExPASy Compute pI/Mw tool.
Paste the accession number into the designated field and click Click here to compute pI/Mw.
Click the Submit button on the next screen.
Read the displayed isoelectric point (pI) value.
Return to the ExPASy tool and paste or type the sequence directly into the input field.
Click Click here to compute pI/Mw again.
Observe the calculated isoelectric point, which you can now use in your experimental design.
For more advanced analyses, consider using the ExPASy Protein Tools suite, which offers additional features such as molecular weight calculation and pH-dependent properties.
