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Protein MW & pI Calculator

Calculate molecular weight, isoelectric point, extinction coefficient, amino acid composition, and GRAVY score from a protein sequence. Data never leaves your browser.

ProteomicsProtParamClient-Side

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Load example protein data to see the full workflow

Amino acid sequence (one-letter codes)

Paste or type a protein sequence
  • Calculate expected MW for SDS-PAGE and Western blot interpretation
  • Determine pI for isoelectric focusing and ion exchange chromatography planning
  • Compute extinction coefficient for UV absorbance-based protein concentration measurement
  • Analyze amino acid composition and hydropathy profile
  • Predict charge-vs-pH curve for buffer selection in protein purification

Don't use for

  • Proteins with extensive post-translational modifications (glycosylation, phosphorylation) — the tool calculates from primary sequence only
  • Peptide mass fingerprinting from MS data — use Mascot or MaxQuant
  • Protein structure prediction — use AlphaFold or ESMFold

Key Protein Physical Properties

Every protein has physical properties determined by its amino acid sequence:

• Molecular weight: Sum of residue masses + water. Critical for SDS-PAGE interpretation, Western blot ladder selection, and mass spec identification • Isoelectric point (pI): pH of zero net charge. Determines migration in isoelectric focusing, solubility minimum, and optimal ion exchange chromatography conditions • Extinction coefficient (ε₂₈₀): Enables concentration measurement by UV absorbance using Beer-Lambert law: c = A₂₈₀/ε • GRAVY score: Predicts solubility and membrane association tendency

Practical Laboratory Applications

Common uses for these calculations:

• SDS-PAGE: Compare calculated MW with observed migration to detect PTMs, cleavage, or aggregation • Protein purification: Choose ion exchange resin based on pI (anion exchange for pI < buffer pH, cation for pI > buffer pH) • Concentration measurement: Use ε₂₈₀ with A₂₈₀ reading to calculate concentration without Bradford/BCA assays • Expression construct design: Verify expected MW of fusion proteins, tagged constructs, and truncations

Frequently Asked Questions

Next Steps

Electrophoresis Systems

SDS-PAGE and Western blot systems for protein analysis

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Spectrophotometers

UV-Vis spectrophotometers for protein concentration measurement

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