What is recorded
The chemistry that defines a peptide.
A peptide is more than a name. Sequence, covalent shape, mass, and registry numbers are how the same substance is recognized across papers and chemical databases.
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Amino-acid sequence
The order of residues from N-terminus to C-terminus. Non-canonical chemistry — D-amino acids, pyroglutamate, lipidated lysines — is written beside the one-letter string.
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Length and formula
How many amino acids are in the chain, and the elemental composition (C, H, N, O, S) of that covalent structure.
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Molecular weight
Average mass in grams per mole. Peptide bonds lose water; disulfides lose two hydrogens; amides and other termini shift the mass again.
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Chemical identifiers
CAS Registry Numbers and PubChem compound identifiers, when they exist, so the same substance can be matched in the chemical literature.
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Linear or cyclic
Whether the backbone is an open chain or closed by a covalent ring — a disulfide, a thioether, or a head-to-tail peptide bond.
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Modifications
C-terminal amidation, N-terminal pyroglutamate, D-residues, N-methylation, and lipid conjugation change stability, charge, and receptor selectivity.
Peptide bonds
How amino acids become a chain.
Each peptide bond is an amide formed when the carboxyl group of one amino acid condenses with the amino group of the next, releasing water. Length counts residues, not bonds: an n-residue peptide has n − 1 peptide bonds.
Topology
Linear chains and covalent rings.
Many hormones are linear polymers. Others — oxytocin, insulin, somatostatin — are cyclic because a disulfide or another covalent link closes a ring. Classification here follows covalent topology, not whether the chain folds into a helix in water.
Terminals
Why the ends of a peptide matter.
Native ribosomal peptides usually begin with a free amine and end with a free acid. Many bioactive peptides are C-terminally amidated, start as pyroglutamate, or carry other end-group chemistry that shifts mass and resists proteases.
How to look something up
Start from sequence, name, or identifier.
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1
Identify the peptide
Enter a stretch of one-letter sequence, a common name, a CAS number, or a PubChem identifier.
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2
Restrict by chemistry
Limit results by molecular weight, residue count, linear versus cyclic structure, and known modifications.
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3
Check the sources
Each entry cites primary literature or a public chemical record so sequence and mass can be confirmed independently.
Notation
How peptide sequences are written.
One-letter and three-letter amino-acid codes, peptide-bond condensation, terminal amides, and the arithmetic behind molecular weight — the conventions used throughout this database.
Sequence notation guide
How this database writes peptide sequences, including chains, disulfides, D-residues, and terminal groups.
Amino acid abbreviations
Standard 20 amino acids with 1-letter codes, 3-letter codes, and residue masses.
Molecular weight calculations
How peptide mass is computed from residues, water loss, disulfides, and terminal groups.
1-letter vs 3-letter codes
When to use one-letter FASTA-style codes versus three-letter residue names.
Scope
A reference, not a product list.
Values here are for scientific look-up. They are not medical advice and not an offer to sell any substance. Chemical identifiers link out to public registries for independent verification.