title: GTP modulates [125I]iodomelatonin binding to a picomolar-affinity site in the Syrian hamster hypothalamus.
abstract: Saturation binding experiments conducted with [125I]iodomelatonin at 0-4 degrees C in the Syrian hamster hypothalamus, revealed a single nanomolar-affinity site which was not affected by GTP. In contrast, incubation at 30 degrees C revealed two distinct binding sites with picomolar and nanomolar affinities, respectively. GTP caused a significant decrease in the affinity of only the picomolar site but did not alter its density; control: Kd = 43 +/- 6 pM, Bmax = 1.7 +/- 0.3 fmol/mg protein; GTP (1 mM): Kd = 250 +/- 52, Bmax = 3.9 +/- 2.6 fmol/mg protein. The foregoing indicates that the affinity of the putative melatonin receptor in the hamster hypothalamus is modulated by a regulatory G protein.
authors.affiliation: Department of Biomedical Sciences, McMaster University, Ontario, Canada.
authors.forename: L P
authors.initials: LP
authors.lastname: Niles
mesh_terms: D000818:Animals; D001665:Binding Sites; D006224:Cricetinae; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism / Q000648:ultrastructure*; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D008647:Mesocricetus; D009711:Nucleotides / Q000494:pharmacology; D013696:Temperature
chemical_list: D007457:Iodine Radioisotopes; D009711:Nucleotides; D006160:Guanosine Triphosphate; C044556:2-iodomelatonin; D008550:Melatonin