Educational resource
Educational resources
This section explains the conventions used on every compound record: how sequences are written, what residue codes mean, how peptide bonds and termini affect formula and mass, and how to search the directory without misreading a field.
Peptide Sequence Database is a lookup tool, not a textbook or a prescribing reference. The guides below are practical companions to the fields you will see on each record — 1-letter sequence, display notation, length, molecular formula, molecular weight, classification, modifications, CAS number, and PubChem CID.
What you will find here
- Sequence notation — how searchable 1-letter strings relate to human-readable display notation, including disulfides, D-residues, and terminal groups
- Amino-acid abbreviations — the twenty proteinogenic residues with 1-letter and 3-letter codes and residue masses
- 1-letter vs 3-letter codes — when each alphabet is appropriate and where conversion loses information
- Peptide bonds — condensation chemistry, length versus bond count, and rings that are not peptide bonds
- Terminal modifications — amidation, pyroglutamate, ethylamides, amino alcohols, and deamino termini
- Molecular weight — how average mass relates to residues, water loss, disulfides, and salts
- Structural classification — how linear versus cyclic is assigned
- How to use this database — search, filters, and independent verification via PubChem and CAS
How to read a compound record
Start with the display notation and modifications when a peptide is chemically unusual. Use the 1-letter sequence for search and quick comparison. Confirm identity with the CAS number and PubChem link before laboratory or regulatory use. Values on this site are curated from public sources and can contain curation errors or differ by convention (free base versus salt, average versus monoisotopic mass).
Open any guide from the sidebar. Each page is written so you can return to it while comparing records in the compound directory.