peptide-qc

Inspectable, deterministic quality-control calculations for a standard 20-amino-acid peptide sequence.

The package reports:

• normalized sequence and residue composition;
• elemental formula and average/monoisotopic molecular mass;
• explicit modification mass deltas, without pretending to infer an unknown modification structure;
• approximate net charge at a requested pH and an approximate isoelectric point;
• Kyte–Doolittle hydropathy values and a smoothed profile.

Install

npm install peptide-qc

Library usage

import { analyzePeptide } from "peptide-qc";

const result = analyzePeptide("ACDEFGHIK", {
  pH: 7,
  hydropathyWindowSize: 7,
  modifications: [{ name: "phosphorylation", deltaMassDa: 79.966331 }],
});

console.log(result.mass.monoisotopicDa);
console.log(result.charge.netCharge);

Whitespace and hyphens are accepted as display separators. The parser rejects non-standard or ambiguous residue codes instead of silently guessing.

CLI

npx peptide-qc analyze \
  --sequence ACDEFGHIK \
  --ph 7 \
  --window-size 7 \
  --json

One explicit modification mass can be supplied with --modification phosphorylation=79.966331. The output is deterministic JSON and the CLI does not access the network.

Scientific assumptions and limits

Mass is calculated as the sum of standard amino-acid residue formulas plus water. Average and monoisotopic values use the elemental constants in the source. A supplied deltaFormula is used to calculate a modification mass; a supplied deltaMassDa is kept as an explicit mass delta when the structure is not represented.

Net charge and pI are transparent approximations using fixed pKa values for the termini and ionizable side chains. They do not model solvent, temperature, ionic strength, aggregation, unusual residues, disulfide connectivity, cyclization, terminal caps or instrument-specific ion chemistry. Hydropathy is the Kyte–Doolittle scale and is not a solubility or formulation prediction.

This is research-use-only and educational software. It does not certify a batch, replace a validated analytical method, identify an unknown, provide a therapeutic dose or give clinical advice. The package is maintained by Péptido México, a commercial supplier of research materials; that relationship is disclosed here and in CITATION.cff.

References

• Kyte J, Doolittle RF. A simple method for displaying the hydropathic character of a protein. J Mol Biol. 1982;157(1):105–132. https://doi.org/10.1016/0022-2836(82)90515-0
• Bjellqvist B, et al. The focusing positions of polypeptides in immobilized pH gradients can be predicted from their amino acid sequences. Electrophoresis. 1993;14(1):1023–1031. https://doi.org/10.1002/elps.11501401163

Development

npm test
npm run pack:check

Fixtures use synthetic sequences. Do not add customer data, private batch records or real certificates of analysis.

The latest suite release is archived on Zenodo with reproducible citation metadata.

Citation

See CITATION.cff and cite the exact release when possible.