Single-site binding, free ligand and affinity
For a reversible one-to-one receptor/ligand interaction at equilibrium, the dissociation constant relates free receptor, free ligand and complex concentrations.
Key knowledge
For a reversible one-to-one receptor/ligand interaction at equilibrium, the dissociation constant relates free receptor, free ligand and complex concentrations. Occupancy is hyperbolic in free ligand and reaches one-half when free ligand equals Kd. Substituting total ligand for free ligand requires a depletion assessment; washed pull-down material need not retain the original equilibrium.
Values and equations
Kd = [R][L]/[RL]; θ = [RL]/([R]+[RL]) = [L]/(Kd+[L])
- Kd
- conditional concentration-based dissociation constant mol m⁻³
- [R],[L],[RL]
- free receptor, free ligand and complex concentrations mol m⁻³
- θ
- fraction of active single sites occupied 1
Conditions and scope
- Use a single binding-site model with active species and equilibrium reached.
- Concentration-based Kd has concentration units and depends on conditions; it is not an unqualified dimensionless thermodynamic standard-state constant.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read equations4/5/7, free-versus-total/depletion and disturbed-equilibrium paragraphs; excluded fixed association-rate ranges and logarithm of a dimensional constant without standard-state conversion.
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Entry details
Permanent link to this entry ↗- Record identity
- uni-chem-ligand-binding-equilibrium
- Revision
- core.1
- Structured reference record
- University core expansion