1. Any individual atom, group, or molecule attached to a central metal ion by multiple coordinate bonds; e.g., the porphyrin portion of heme, the corrin nucleus of the B12 vitamins. 2. An organic molecule attached to a tracer element, e.g., a radioisotope. 3. A molecule that binds to a macromolecule, e.g., a l. binding to a receptor. 4. The analyte in competitive binding assays, such as radioimmunoassay. 5. An atom or group covalently attached to a specified carbon atom in an organic molecule. [L. ligo, to bind]
- Fas l. a molecule on the surface of cytotoxic T cells that binds to its receptor, Fas, on the surface of other cells, initiating apoptosis in the target cell.
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li·gand 'lig-ənd, 'līg- n a group, ion, or molecule coordinated to a central atom or molecule in a complex
li·gand·ed -əd adj
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n.
a molecule that binds to another molecule, as in antigen-antibody and hormone-receptor bondings.
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li·gand (liґgand) (ligґənd) [L. ligare to tie or bind] 1. a molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. 2. a molecule that donates or accepts a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex.Medical dictionary. 2011.