Enter a peptide sequence in standard 1-letter amino-acid code to calculate molecular weight, empirical formula, net charge, isoelectric point, and extinction coefficient. Everything runs in your browser.
Calculated as a linear peptide with free N- and C-termini (one water added). Disulfide bonds, cyclisation, and chemical modifications are not accounted for. Research use.
Net charge and pI use a consensus side-chain pKa set (Asp 3.65, Glu 4.25, His 6.00, Cys 8.18, Tyr 10.07, Lys 10.53, Arg 12.48; N-term 8.0, C-term 3.1). ε₂₈₀ from Trp (5500) and Tyr (1490) M⁻¹cm⁻¹, assuming reduced cysteines.
Average mass uses natural isotope abundances — what you weigh on a balance. Monoisotopic uses only the most common isotope of each element — what you see as the main peak in high-resolution mass spec (for peptides under ~2 kDa).
Net charge at pH 7.4 predicts behaviour in physiological conditions; strongly positive peptides tend to interact with cell membranes. At its pI a peptide has minimum solubility, so buffers are kept 1–2 pH units away.
Lets you convert a UV absorbance at 280 nm into concentration (Beer-Lambert). Comes mainly from tryptophan and tyrosine. Peptides with no W or Y have ε₂₈₀ ≈ 0 and need another method (BCA, amino-acid analysis).
Educational and reference use only. Not medical advice. Research Use Only.