Isoelectric Point (pI) Calculator
Determine the isoelectric point (pI) of a peptide or protein sequence by calculating net electrical charge across pH 1-14.
Input Parameters
Enter details for calculation.
Isoelectric Point (pI)
Net Charge at pH 7.40
Expert Tip
At its isoelectric point, a protein carries no net charge, which significantly reduces its electrostatic repulsion and solubility, often leading to precipitation.
Calculation Methodology & Details
Formula
The pKa values used: N-term: 9.6, C-term: 2.34, K: 10.5, R: 12.4, H: 6.0, D: 3.9, E: 4.2, C: 8.3, Y: 10.1. A bisection algorithm solves for net charge = 0.
Important Disclaimer
The calculations provided are for educational and general planning guidelines only. They do not replace professional laboratory or environmental analysis or certified scientific advice.
How pI is Calculated
Steps to solve for the peptide isoelectric point:
Count Residues
The peptide sequence is scanned to count ionizable amino acids.
Calculate Charges
At any pH, acidic groups carry a negative charge and basic groups carry a positive charge.
Iterate pH levels
The bisection algorithm searches from pH 1 to 14 to locate the exact zero-charge transition.