A term used to describe a substance (the ligand) that has the capacity for specific and noncovalent (reversible) binding to some protein. A ligand may be a coenzyme for a specific enzyme. The ligand can be covalently attached (immobilized) by means of the appropriate chemical reaction to the surface of certain porous column material. When a mixture of proteins containing the enzyme to be isolated is passed through the column, the enzyme, which is capable of tightly binding to the ligand, does so, and is in this manner held to the column. The other proteins present, which have no specific affinity for the ligand, pass on through the column. The protein/ligand complex is then dissociated and the enzyme eluted from the column, which may be accomplished by passing more free (unbound) coenzyme through the column. The ligand may be hormones (i.e., used to isolate receptor molecules) or any other type of molecule that is capable of binding specifically and reversibly to the desired protein or protein complex.
Substance that binds to a receptor.
Molecule or chemical bound to another chemical group or molecule; following a chemical reaction, the ligand typically emerges unchanged chemically.