Research concepts
Why EC50 and affinity are not equivalent
EC50, affinity and receptor reserve: Am I comparing a functional response or a binding measurement?
Source editorial review:
Before interpreting the result
Am I comparing a functional response or a binding measurement?
- Copy the parameter with its units: EC50, Kd and other estimates are not interchangeable labels.
- Identify the receptor, cellular system and response used to fit the curve.
- Check whether receptor expression or reserve differed between conditions.
EC50, affinity and receptor reserve
EC50 locates the concentration associated with half of a defined response on a curve. Affinity describes a binding interaction and is estimated through different parameters and assumptions. Receptors, coupling and amplification lie between binding and response, so two systems can yield different EC50 values for the same ligand. Receptor reserve can further separate required occupancy from the observed response.
A reading case: what to check
Imagine two reports with different EC50 values and the same compound name. Check whether they measured the same cellular output, receptor and comparable conditions before attributing the difference to the material. If one reports Kd and the other EC50, keep separate columns. The table can explain what each assay measured, not which product is 'stronger' in every setting.
What to preserve in the record
A lower EC50 does not by itself establish higher affinity. In the review table, separate binding from functional parameters and compare each within compatible systems.
Questions and answers
Am I comparing a functional response or a binding measurement?
EC50 locates the concentration associated with half of a defined response on a curve. Affinity describes a binding interaction and is estimated through different parameters and assumptions. Receptors, coupling and amplification lie between binding and response, so two systems can yield different EC50 values for the same ligand. Receptor reserve can further separate required occupancy from the observed response.
What should the review record preserve?
A lower EC50 does not by itself establish higher affinity. In the review table, separate binding from functional parameters and compare each within compatible systems.