Isoelectric Point (pI) Calculator
Isoelectric Point (pI) Calculator
This tool estimates the isoelectric point (pI) of a protein or peptide based on its amino acid sequence. It helps biochemistry students, lab researchers, and molecular biologists understand at which pH a molecule carries no net electrical charge.
Users input a 1-letter amino acid sequence (e.g., MENSDSEQNFLKAVNEK) and the tool calculates the net charge at varying pH values using the charge balance method. Side-chain dissociation constants (pK values) for charged residues are used, including:
- Basic groups – K, R, H
- Acidic groups – D, E, C, Y
- Terminal groups – N-terminal and C-terminal
The algorithm performs a binary search between pH 2 to 14 to find the pH where the net charge becomes zero. This pH is returned as the isoelectric point (pI) to four decimal places.
Features include:
- Sample sequence autofill
- Error alerts for invalid inputs
- Quick result display with net charge balancing
- Supports standard 20 amino acids (excluding selenocysteine)
It's suitable for predicting solubility behavior, electrophoresis migration, and optimal pH conditions for purification of peptides or proteins in lab experiments.