Pharmacodynamics

Ligand

Any molecule, such as a drug, hormone or neurotransmitter, that binds to a specific site on a receptor or other macromolecule; binding alone does not imply activation or blockade.

In depth

Ligands are classified by what follows binding: agonists (full or partial) activate the receptor, neutral antagonists occupy it without activating it, inverse agonists reduce constitutive activity, and allosteric modulators bind at a site distinct from the orthosteric (endogenous ligand) site to alter affinity or efficacy. Endogenous ligands include neurotransmitters, hormones and autacoids; exogenous ligands include drugs and toxins.

Most drug binding is reversible and obeys the law of mass action, its strength being expressed by the equilibrium dissociation constant (Kd). Radiolabelled ligands are used in binding assays to measure receptor density (Bmax) and affinity.

TRIn Turkish

Ligand

Bir reseptör veya başka bir makromolekül üzerindeki belirli bir bölgeye bağlanan ilaç, hormon ya da nörotransmiter gibi her türlü moleküldür; bağlanma tek başına aktivasyon veya blokaj anlamına gelmez.

Ligandlar, bağlanmanın ardından ortaya çıkan sonuca göre sınıflandırılır: agonistler (tam veya kısmi) reseptörü aktive eder, nötr antagonistler reseptörü aktive etmeden işgal eder, ters agonistler konstitütif aktiviteyi azaltır, allosterik modülatörler ise ortosterik (endojen ligand) bölgeden farklı bir bölgeye bağlanarak afiniteyi veya etkinliği değiştirir. Endojen ligandlar nörotransmiterleri, hormonları ve otakoidleri; eksojen ligandlar ise ilaçları ve toksinleri kapsar.

İlaç bağlanmasının çoğu geri dönüşümlüdür ve kütle etkisi yasasına uyar; bağlanmanın gücü denge disosiyasyon sabitiyle (Kd) ifade edilir. Radyoaktif işaretli ligandlar, reseptör yoğunluğunu (Bmax) ve afiniteyi ölçmek için bağlanma deneylerinde kullanılır.

Updated 24.09.2026 1 views Educational reference — verify against current sources before clinical use.

Read next

ReceptorReseptör

A macromolecule, usually a protein, to which a drug or endogenous ligand binds specifically and thereby initiates a change in cell function that produces a biological response.

 AgonistAgonist

A drug or endogenous substance that binds to a receptor and activates it, producing a biological response; it possesses both affinity and efficacy (intrinsic activity).

 AntagonistAntagonist

A drug that binds to a receptor or other target without activating it (affinity but no efficacy) and thereby prevents or reduces the response to an agonist.

 Allosteric ModulatorAllosterik Modülatör

A ligand that binds to a site on a receptor distinct from the orthosteric (endogenous agonist) site and changes the receptor's affinity for, or response to, the orthosteric agonist.

 Dissociation ConstantDisosiyasyon Sabiti

The equilibrium constant for dissociation of a drug–receptor complex, equal to the free drug concentration at which half of the receptors are occupied at equilibrium; a lower Kd means higher affinity.

 AffinityAfinite

The strength of binding between a drug and its receptor or target, determined by the rates of association and dissociation and usually expressed as the equilibrium dissociation constant (Kd) or its negative logarithm (pKd).