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Peptide sequence properties

Enter a sequence to get its molecular formula, molecular weight, isoelectric point and net charge.

One-letter (GEPPPGKPADDAGLV) or three-letter with hyphens (H-Gly-Glu-Pro-OH). D- prefixes, Aib, Nle, Orn, pGlu, Dmt and 2Nal are recognised.

Needs two or more Cys

Sequence
H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH
Residues
7
Molecular formula
C33H57N11O9
Average mass
751.87 g/mol
Monoisotopic mass
751.4341 Da
Isoelectric point
11.65
Net charge at pH 7
+1.98
Extinction coeff. (280 nm)
No Trp, Tyr or cystine: not measurable at 280 nm
+3+2+10-102468101214
Net charge against pH. The dashed line marks pH 7; the circle marks the pI (11.65).

Composition

  • Pro ×3
  • Thr ×1
  • Lys ×1
  • Arg ×1
  • Gly ×1

How it's calculated

Mass. The molecular formula is the sum of the residue formulas plus one water, adjusted for the termini (acetyl adds C₂H₂O; a C-terminal amide swaps OH for NH₂) and for each disulfide bridge (minus two hydrogens). Average mass uses IUPAC standard atomic weights; monoisotopic mass uses the most abundant isotope of each element. Salts and counter-ions such as TFA or acetate are not included, so a lot's gross weight will differ.

Isoelectric point and charge. Net charge is the Henderson–Hasselbalch sum over every ionisable group, using the EMBOSS pKa set: N-terminus 8.6, C-terminus 3.6, Asp 3.9, Glu 4.1, His 6.5, Cys 8.5, Tyr 10.1, Lys 10.8 and Arg 12.5. The pI is the pH at which that sum is zero. Cysteines in disulfide bridges are treated as non-ionisable. Real pKa values shift with neighbouring residues, folding and solvent, so treat both figures as estimates.

Extinction coefficient. The molar absorptivity at 280 nm in water, from Pace et al. (1995): 5,500 per Trp, 1,490 per Tyr and 125 per cystine.

D- and L-isomers share a formula, so D-residues give the same results. Lowercase one-letter codes are read as D-residues.