Analyze biochemical and physical parameters of your protein sequences
Input Protein Sequence
Only standard amino acid characters are accepted.
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Our Protein Isoelectric (pI) Point Calculator is a specialized, web-based tool designed to determine the essential biochemical and physical properties of your protein sequences. You can instantly calculate its theoretical isoelectric point (pI), molecular weight, amino acid composition, and other vital parameters by simply providing a sequence. This tool is invaluable for researchers planning protein purification strategies (like isoelectric focusing and ion-exchange chromatography), predicting protein behavior in electrophoresis, and gaining fundamental insights into protein function.
How to Use
- Input Sequence: Paste your protein sequence into the text box. The sequence should contain only standard single-letter amino acid codes.
- Analyze: Click the “Analyze Sequence” button to process your data.
- Review Results: The tool will instantly display a comprehensive report of the calculated parameters for your protein.
Tip: Before pasting, ensure your sequence is in a plain text format and does not contain any headers, numbers, or non-standard characters for the most accurate results.
How is the Protein Isoelectric Point (pI) Calculated?
The isoelectric point (pI) is the specific pH at which a protein has a net charge of zero. At a pH below its pI, a protein will have a net positive charge; above its pI, it will have a net negative charge.
The calculation is an iterative process that finds the pH where the protein’s total charge is closest to zero. This is achieved by:
- Identifying all ionizable groups in the protein: the N-terminal amino group, the C-terminal carboxyl group, and the side chains of seven amino acids (Aspartic acid, Glutamic acid, Cysteine, Tyrosine, Histidine, Lysine, and Arginine).
- Using a set of standard pKa values for each of these groups, the algorithm calculates the charge of each group at a given pH.
- The charges of all groups are summed to get the net charge of the entire protein at that specific pH.
- This process is repeated across a wide pH range (typically 0-14) until the pH that results in a net charge of zero is identified. This pH value is reported as the theoretical pI.
Features and Outputs
This protein parameters analyzer provides the following comprehensive outputs:
- Amino Acid Composition: Provides the absolute count and percentage frequency for each of the 20 standard amino acids.
- Molecular Weight (MW): Calculates the molecular weight of the protein sequence based on the average isotopic masses of the amino acids.
- Theoretical Isoelectric Point (pI): Estimates the pH at which the protein has a net neutral charge, which is crucial for purification and electrophoresis methods.
- Amino Acid Property Groups: Classifies and totals amino acids based on their chemical properties (e.g., Hydrophobic, Polar, Positively Charged, Negatively Charged).
- Atomic Composition: Provides the total count of each type of atom (Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur) that constitutes the protein.
- Extinction Coefficient: Estimates the molar absorption coefficient of the protein at 280 nm, which is useful for determining protein concentration via UV spectroscopy.
- Estimated Half-Life: Offers a prediction of the protein’s stability and lifespan within different biological systems (mammalian, yeast, and E. coli).
- Instability Index: Computes an index to predict the stability of the protein in a test tube. A value below 40 indicates a stable protein.
- Aliphatic Index: Calculates the relative volume of the protein occupied by aliphatic side chains (Alanine, Valine, Isoleucine, and Leucine), which is correlated with thermostability.
- Grand Average of Hydropathicity (GRAVY): A score representing the overall hydrophobicity of the protein. Positive values indicate a hydrophobic nature, while negative values suggest a hydrophilic nature.
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References & Suggested Reading
Kozlowski LP. IPC – Isoelectric Point Calculator. Biol Direct. 2016 Oct 21;11(1):55. doi: 10.1186/s13062-016-0159-9. PMID: 27769290; PMCID: PMC5075173.
Meet the Authors
Mahdi Morshedi Yekta
Founder & Bioinformatics Developer
Mahdi is the founder of ScienceCodons and a Medical Biotechnologist with a deep passion for computational biology. Holding an M.Sc. in Medical Biotechnology, he specializes in transforming complex biological algorithms into accessible, high-performance web tools, bridging the gap between laboratory sciences and software engineering.
Fatemeh Faryadras
Medical Biotechnologist & Researcher
Fatemeh is a Medical Biotechnologist and researcher. With extensive expertise in genetic engineering, molecular cloning, and cancer biology, she combines her rigorous laboratory background with intuitive design principles to create reliable, user-centered scientific calculators and tools.
Dr. Mosayeb Rostamian
Assistant Professor, Infectious Diseases Research Center
Certified Scientific Reviewer
Google ScholarExpert Review Process
To ensure the highest quality and scientific accuracy, this tool's underlying algorithms, formulas, and edge-case handling have been thoroughly reviewed and validated by Dr. Mosayeb Rostamian.
The "Reviewed By" badge signifies that an independent expert has evaluated the tool's logic to guarantee accuracy and alignment with the current consensus in the scientific community.