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Glossary of Pharmacology 

Inhibitory constant (Ki) 

Definition: 
The inhibitory constant (Ki) is a type of equilibrium dissociation constant (Kd) that represents the equilibrium binding affinity for a ligand that reduces the activity of its binding partner. Krepresents the concentration at which the inhibitor ligand occupies 50% of the receptor sites when no competing ligand is present. The smaller the Ki the greater the binding affinity and the smaller the amount of ligand is needed to inhibit its binding partners activity. 

Linked terms:  Equilibrium dissociation constant (Kd), ligand, binding affinity    

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