Guanine nucleotide-binding protein regulation of melatonin receptors in lizard brain

Journal Article · Mon May 01 00:00:00 EDT 1989 · Proceedings of the National Academy of Sciences of the United States of America; (USA)

DOI:https://doi.org/10.1073/pnas.86.10.3882· OSTI ID:5185879

Rivkees, S A; Carlson, L L; Reppert, S M ^[1]

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1. Harvard Medical School, Boston, MA (USA)

Melatonin receptors were identified and characterized in crude membrane preparations from lizard brain by using {sup 125}I-labeled melatonin ({sup 125}I-Mel), a potent melatonin agonist. {sup 125}I-Mel binding sites were saturable; Scatchard analysis revealed high-affinity and lower affinity binding sites, with apparent K{sub d} of 2.3 {plus minus} 1.0 {times} 10{sup {minus}11} M and 2.06 {plus minus} 0.43 {times} 10{sup {minus}10} M, respectively. Binding was reversible and inhibited by melatonin and closely related analogs but not by serotonin or norepinephrine. Treatment of crude membranes with the nonhydrolyzable GTP analog guanosine 5{prime}-({gamma}-thio)triphosphate (GTP({gamma}S)), significantly reduced the number of high-affinity receptors and increased the dissociation rate of {sup 125}I-Mel from its receptor. Furthermore, GTP({gamma}S) treatment of ligand-receptor complexes solubilized by Triton X-100 also led to a rapid dissociation of {sup 125}I-Mel from solubilized ligand-receptor complexes. Gel filtration chromatography of solubilized ligand-receptor complexes revealed two major peaks of radioactivity corresponding to M{sub r} > 400,000 and M{sub r} ca. 110,000. This elution profile was markedly altered by pretreatment with GTP({gamma}S) before solubilization; only the M{sub r} 110,000 peak was present in GTP({gamma}S)-pretreated membranes. The results strongly suggest that {sup 125}I-mel binding sites in lizard brain are melatonin receptors, with agonist-promoted guanine nucleotide-binding protein (G protein) coupling and that the apparent molecular size of receptors uncoupled from G proteins is about 110,000.

• OSTI ID: 5185879
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America; (USA), Vol. 86:10; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
MELATONIN
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RECEPTORS
MOLECULAR STRUCTURE
BIOCHEMICAL REACTION KINETICS
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CELL MEMBRANES
GUANINE
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LIGANDS
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MEMBRANE PROTEINS
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ANIMALS
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HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
INDOLES
INTERMEDIATE MASS NUCLEI
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
NERVOUS SYSTEM
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
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550601* - Medicine- Unsealed Radionuclides in Diagnostics