Isoelectric Point (pI)
Also known as: pI · isoelectric point
The pH at which a peptide carries no net charge — where it is least soluble, affecting handling and purification.
The isoelectric point (pI) is the pH at which a peptide’s positive and negative charges balance to zero net charge. It is set by the mix of acidic and basic side chains in the sequence.
It matters practically because a peptide is typically least soluble near its pI and may come out of solution, and because charge-based purification (chromatography) exploits the difference between a peptide’s pI and the buffer pH.
RELATED TERMS
Side Chain (R Group)
The variable "R group" on each amino acid that gives it its chemical character — charge, size and water-affinity.
Amino-Acid Sequence
The specific order of amino-acid residues in a peptide — its "primary structure" — which dictates shape and activity.
Chromatography
A family of techniques that separate a mixture’s components by how they move through a medium — the basis of HPLC.
Purity
The percentage of a sample that is the intended peptide, as measured by HPLC — the headline quality figure.
Hydrophobic / Hydrophilic
Whether a peptide (or its parts) is attracted to water or repelled by it — a key driver of solubility and folding.
Educational content, not medical advice. All products supplied for research purposes only — not for human consumption.