Physicochemical

Peptide property calculator

Q: What is the isoelectric point used for?

It is the pH where the peptide has no net charge, which guides buffer choice and predicts where solubility tends to be lowest.

Q: Why are there two extinction-coefficient figures?

Cysteines can pair into disulfide bonds (cystines) that absorb slightly. One figure assumes they pair; the other assumes they stay reduced.

Q: Are the calculated peptide properties exact?

They are theoretical, from the sequence alone. Real-world modifications, salt forms, and counter-ions are not included.

Paste an amino-acid sequence in one-letter code and get the core physicochemical properties: molecular weight, isoelectric point, net charge at a chosen pH, the extinction coefficient at 280 nm, and average hydrophobicity (GRAVY).

Sequence ?

—

Net charge at pH?

Molecular weight (average)—

Isoelectric point (pI)—

Net charge at pH 7.4—

Extinction coeff. ε₂₈₀ (cystines)—

ε₂₈₀ (reduced Cys)—

GRAVY (hydropathy)—

Who this is for

This one is aimed at researchers working from a peptide's amino-acid sequence. If you're just preparing a vial, you won't need it — the reconstitution and purity tools cover that. Here, the properties are theoretical: calculated from the sequence alone, before any modifications, salts, or counter-ions.

How to use it

SequencePaste the sequence in one-letter code — each capital letter is one amino acid (G = glycine, K = lysine, and so on). Spaces, numbers, and line breaks are ignored.
Net charge at pHThe pH to evaluate the overall charge at. 7.4 (close to physiological) is a common default; change it to see how charge shifts.

Reading your results

Molecular weightThe mass of one molecule, in daltons (Da).
Isoelectric point (pI)The pH at which the peptide carries no overall charge. Handy for choosing buffers and gauging where it may be least soluble.
Net chargeThe overall electrical charge at your chosen pH — positive, negative, or near zero.
Extinction coeff.How strongly the peptide absorbs UV light at 280 nm. It's the number the A280 tool uses to turn an absorbance reading into a concentration. Two figures: assuming cysteines pair into disulfide bonds (cystines) or not (reduced).
GRAVYAverage "water-loving vs water-repelling" score: negative is more hydrophilic (water-loving), positive is more hydrophobic.

A worked example

BPC-157, sequence GEPPPGKPADDAGLV:

MW 1419.55 Da · pI 3.68 · net charge at 7.4 −2

ε₂₈₀ 0 (no Trp, Tyr or Cys) · GRAVY −0.693

Common questions

What is one-letter code?

A shorthand where each amino acid is a single capital letter (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, V). Sequences are usually published this way.

What is the isoelectric point used for?

It tells you the pH where the peptide has no net charge, which guides buffer choice and predicts where solubility tends to be lowest.

Why are there two extinction-coefficient figures?

Cysteines can pair into disulfide bonds (cystines), which absorb slightly. One figure assumes they pair; the other assumes they stay reduced (unpaired).

Are these values exact?

They're theoretical, from the sequence alone. Real-world modifications, salt forms, and counter-ions aren't included.

The math, for the curious

MW: sum of average residue masses + one water (18.015). Net charge: Henderson–Hasselbalch over the N-terminus, C-terminus, and ionizable side chains (D, E, C, Y, H, K, R). pI: the pH where net charge crosses zero, by bisection. ε₂₈₀: nTyr×1490 + nTrp×5500 + nCystine×125. GRAVY: mean Kyte–Doolittle hydropathy.