Protein Properties Calculator
A free online protein properties calculator that computes molecular weight, isoelectric point (pI), molar extinction coefficient at 280 nm, amino acid composition, and GRAVY hydropathicity score from any amino acid sequence. Includes presets for common proteins like insulin, GFP, and BSA — all computed instantly in your browser with no sequence data uploaded.
Amino Acid Count: 0
Protein Presets
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What is a Protein Properties Calculator?
A protein properties calculator computes key physicochemical properties of a protein from its amino acid sequence. These include molecular weight (MW), isoelectric point (pI) — the pH at which the protein carries no net charge — molar extinction coefficient at 280 nm for UV spectrophotometry, amino acid composition analysis, and the GRAVY (Grand Average of Hydropathicity) score indicating overall hydrophobicity. These properties are essential for experiment planning in protein purification, SDS-PAGE analysis, and spectrophotometric quantification.
How to Use This Calculator
- Enter or paste your amino acid sequence in 1-letter code format (spaces and numbers are automatically removed)
- Or select a preset protein like insulin, GFP, or lysozyme
- Click Analyze to compute all properties instantly
- View molecular weight, pI, extinction coefficient, GRAVY score, and full composition table
- Use the extinction coefficient to calculate protein concentration from A280 readings
Frequently Asked Questions
How is the isoelectric point (pI) calculated?
The pI is calculated using the Henderson-Hasselbalch equation by summing charges from all ionizable groups (N-terminus, C-terminus, Asp, Glu, Cys, His, Lys, Arg, Tyr) across a pH range. A binary search algorithm finds the pH at which the net charge equals zero. Standard pKa values from Lehninger are used.
What does the extinction coefficient tell me?
The molar extinction coefficient at 280 nm (ε₂₈₀) tells you how strongly the protein absorbs UV light at 280 nm, primarily due to tryptophan (Trp), tyrosine (Tyr), and disulfide bonds (Cys-Cys). Using Beer-Lambert law (A = εlc), you can calculate protein concentration from absorbance readings. The Pace method gives: ε₂₈₀ = (nTrp × 5500) + (nTyr × 1490) + (nCys-Cys × 125).
What is the GRAVY score?
GRAVY (Grand Average of Hydropathicity) is the mean of the Kyte-Doolittle hydropathicity values for all amino acids in the sequence. Positive values indicate hydrophobic proteins (e.g., membrane proteins), and negative values indicate hydrophilic (soluble) proteins. Most soluble globular proteins have GRAVY scores between -0.4 and +0.4.