Notes on...

Calculating the isoelectric point, pI

The isoelectric point, pI, is the pH at which the net charge of the peptide is zero. Innovagen's Peptide Calculator first calculates the net charge for pH 7.0. If the charge is > 0 the next pH to check is 7 + 3.5, if the charge is < 0 then pH 7 - 3.5 is checked. This is repeated, using increments/decrements half the size of the previous, until the charge found equals 0, or is sufficiently close to 0.

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