The isoelectric point is the pH at which a peptide carries no net electrical charge. Enter a sequence to calculate the pI, plot the pH-vs-charge curve, and read the charge at any pH.
Consensus pKa set: Asp 3.65, Glu 4.25, His 6.00, Cys 8.18, Tyr 10.07, Lys 10.53, Arg 12.48; N-terminus 8.0, C-terminus 3.1. Computed pI assumes an unstructured peptide and can differ from experimental values.
Curve: net charge from pH 0 to 14. It crosses zero at the pI.
Dominated by Asp (D) and Glu (E). Negatively charged at physiological pH. Insulin ~5.3, serum albumin ~4.7.
A balanced mix of acidic and basic residues, or mostly non-ionisable ones. Minimal charge at physiological pH.
Dominated by Arg (R), Lys (K), His (H). Positively charged at physiological pH — common among antimicrobial and cell-penetrating peptides. LL-37 ~11.1.
Educational and reference use only. Not medical advice. Research Use Only.