Lexicon · NucLex for innovators
Peptide
Fully specified name: Peptide (concept)
A molecule of amino-acid residues joined by peptide bonds.
- Scope note
- A sequence analogy does not predict behavior in a person.
- Synonyms
- None recorded as true synonyms in this context.
- Monograph
- Molecular targeting (planned; brief only)
- External mappings
- None recorded. In W0 no mapping to SNOMED CT® or any external authority is asserted for this entry. A future mapping record will carry source system, identifier, version, relation type, evidence, author, confidence where meaningful, and review state.
- Formal status
- Editorial entry only. It is not part of any released ontology and a prose edit here changes no formal definition.
Draft. This entry is an unreviewed draft. Its sources have not been checked by a named person and no domain reviewer has approved it. Treat every claim as provisional.
Notes
A peptide is a chain of amino acids linked by peptide bonds. The boundary between a peptide and a protein is a matter of convention rather than chemistry: short chains are called peptides, long folded chains proteins, and the threshold differs between textbooks and fields. In nuclear medicine, peptides matter because many targeting molecules are peptides or peptide-like compounds that recognize a receptor on a cell surface and can carry a chelated radionuclide.
A peptide's identity has layers that an ontology should keep distinct. The sequence names the order of residues. Modifications, such as cyclization, non-natural residues, and attached chelators or linkers, change the molecule without changing the sequence. The labeled product adds the radionuclide. Two agents can share a sequence and differ in all of the rest, and those differences can alter binding, stability in blood, and route of elimination.
For that reason a sequence resemblance between two peptides, or between a peptide and a natural hormone, is a hypothesis about behavior and not a finding. Receptor affinity, resistance to enzymatic breakdown, uptake by the kidney, and clearance from blood are each measured separately and may not follow the analogy. NucLex records sequence, modification, labeling, and measured properties as separate facts so that none is inferred from another without stated evidence.