reseptorligand

Reseptorligand, or receptor ligand, is a molecule that binds to a receptor and modulates its activity. Binding typically induces a conformational change in the receptor, triggering intracellular signaling or altering function. Ligands can be endogenous, such as neurotransmitters and hormones, or exogenous, such as drugs, toxins, or experimental compounds.

Receptors are diverse: G protein–coupled receptors (GPCRs), ligand-gated ion channels, receptor tyrosine kinases, and intracellular/nuclear receptors. Ligand binding may occur at the orthosteric site, where the natural ligand binds, or at allosteric sites, where binding changes receptor responsiveness without occupying the orthosteric site. Specificity and affinity determine how tightly a ligand binds.

Ligands are classified by their functional effect: agonists activate receptors; antagonists block receptor activation; inverse agonists reduce constitutive receptor activity; partial agonists produce a submaximal response; allosteric modulators alter the magnitude or duration of the response without directly activating or inhibiting the orthosteric site. Functional selectivity (biased agonism) describes ligands that favor certain signaling pathways.

Pharmacological properties include affinity, potency, and efficacy, often summarized by Kd (binding affinity) and EC50 (effective concentration). Kinetics, such as association and dissociation rates, influence duration of effect. Dose–response relationships reflect receptor occupancy and downstream signaling.

Understanding reseptorligander is central to pharmacology and drug discovery, guiding the design of selective ligands with desired therapeutic effects and minimal off-target activity. Classic examples include adrenaline (epinephrine) acting on adrenergic GPCRs, morphine on mu-opioid receptors, and antihistamines as histamine receptor antagonists.