Lexicon · NucLex for innovators
Binding affinity
Fully specified name: Binding affinity (concept)
A characterization of binding strength under specified conditions.
- Scope note
- Reusable values need assay context, units, and a source.
- 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
Binding affinity describes how strongly one molecule associates with another. In the laboratory it is expressed through quantities such as the equilibrium dissociation constant, the inhibition constant, or the half-maximal inhibitory concentration. These are not interchangeable: they come from different experimental designs, rest on different assumptions, and can differ for the same pair of molecules. A number quoted without its type is not usable.
The conditions matter as much as the number. Affinity depends on temperature, buffer, the form of the target (purified protein, membrane preparation, cells, or tissue), the presence of competing molecules, and in radiopharmaceutical work on whether the measured molecule is the labeled compound, the unlabeled precursor, or a surrogate labeled with a different radionuclide. A value from a cell-free assay is not a value in a living person.
Pharmacologists, radiochemists, and computational chemists each report affinity in habitual ways, and a predicted affinity from a docking model is a different kind of claim from a measured one. For NucLex a binding affinity is a parameter attached to an interaction between two named participants. The record carries the quantity type, units, assay system, conditions, uncertainty, source, and version. No affinity value is reproduced in this entry, and no comparison between agents is implied.