Peptide sequence analyzer

Paste a sequence in one-letter code to get its formula, average and monoisotopic mass, the ions you should see in mass spectrometry, isoelectric point, net charge, hydropathy and stability flags.

How the numbers are calculated

Masses are summed from residue formulas plus one water, using IUPAC average atomic weights for the average mass and the most abundant isotopes for the monoisotopic mass. Acetylation adds C₂H₂O, amidation replaces the C-terminal OH with NH₂, and each disulfide removes two hydrogens. Ion m/z values add the mass of a proton per charge.

The isoelectric point uses the EMBOSS pK_a set and a bisection search; acetylated or amidated termini are treated as uncharged. GRAVY is the Kyte–Doolittle mean. The extinction coefficient at 280 nm follows Pace et al. (Trp 5500, Tyr 1490, cystine 125 M⁻¹cm⁻¹). Predicted values are estimates; measured values depend on buffer, counter-ions and modifications.

Using it for an identity check

Compare the [M+H]⁺ or multiply charged ions above with the mass spectrum on a certificate of analysis. A match within the instrument's stated tolerance supports identity; a difference of +16 Da suggests oxidation, +0.98 Da deamidation, and −18 Da a lost water or cyclisation. See HPLC and mass spectrometry explained.

Non-standard residues (Aib, norleucine, naphthylalanine) and cyclic lactams are not supported here; their masses are given on the individual compound pages.