. "\"Interacting selectively and non-covalently with one or more specific sites on a receptor molecule, a macromolecule that undergoes combination with a hormone, neurotransmitter, drug or intracellular messenger to initiate a change in cell function.\" [GOC:bf, GOC:ceb, ISBN:0198506732]" . . "receptor binding" . "Wikipedia:Ligand_(biochemistry)" . . "receptor-associated protein activity" . "receptor ligand" .