Peptide Science
Receptor Pathways: A Researcher's Primer
Binding affinity, efficacy, desensitisation and biased signalling — the four concepts that explain most surprises in peptide receptor work.
August 18, 2026 · 6 min read · Novanta Research
Affinity is not efficacy
Affinity describes how tightly a compound binds; efficacy describes how much response that binding produces. A compound can bind superbly and do almost nothing, which is exactly what a competitive antagonist is.
Published values are usually reported as Kd or Ki for affinity and EC50 for functional potency. Comparing an EC50 from one assay system to a Ki from another is one of the most common misreadings in the peptide literature.
Desensitisation and receptor trafficking
Sustained stimulation leads to receptor phosphorylation, arrestin recruitment, and internalisation. The receptor is pulled off the surface and either recycled or degraded, so the same concentration produces a smaller response over time.
This is why pulsatile and continuous exposure protocols can produce opposite conclusions from the same compound, and why washout periods belong in the method section, not the footnotes.
Biased agonism
One receptor can signal through more than one pathway — classically through G proteins and through arrestins. Some ligands preferentially trigger one branch, which is called biased agonism.
For research design this means the readout you choose partly determines the answer you get. A cyclic AMP assay and an arrestin recruitment assay can rank the same set of compounds differently.
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For laboratory and research use only. Not for human or veterinary consumption. Novanta Research is not a compounding pharmacy and nothing in this article is medical advice or a claim that any compound diagnoses, treats, cures or prevents any condition.