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Hypothalamic binding sites for pituitary adenylate cyclase activating polypeptide: characterization and molecular
P E Gottschall1, I Tatsuno, A Arimura
1U.S.-Japan Biomedical Research Laboratories, Tulane University, Belle Chasse, Louisiana 70037.
Summary
Researchers identified a high-affinity pituitary adenylate cyclase activating polypeptide (PACAP) binding site in the rat hypothalamus. This receptor exhibits greater affinity for PACAP38 than PACAP27, with a molecular weight of 57,000 Da.
Area of Science:
- Neuroendocrinology
- Molecular Pharmacology
Background:
- Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with diverse physiological roles.
- Understanding PACAP binding sites is crucial for elucidating its mechanisms of action in the central nervous system.
Purpose of the Study:
- To identify and characterize PACAP binding sites within the rat hypothalamus.
- To determine the affinity and molecular properties of these binding sites.
Main Methods:
- Radioligand binding assays using [125I]PACAP27.
- Displacement studies with unlabeled PACAP27, PACAP38, VIP, and PACAP(1-23).
- GTP analog studies to assess receptor regulation.
- Covalent cross-linking and SDS-PAGE to estimate receptor molecular weight.
Main Results:
- PACAP27 binding was rapid, reversible, and GTP-regulated.
- PACAP27 and PACAP38 demonstrated high affinity for the binding site, with PACAP38 being more potent (Kd values: PACAP27 = 1452 pM, PACAP38 = 175 pM).
- A 60 kDa peptide-receptor complex was identified, suggesting a receptor molecular weight of approximately 57,000 Da.
Conclusions:
- A specific, high-affinity PACAP binding site exists in the rat hypothalamus.
- The receptor displays preferential binding for PACAP38 over PACAP27.
- The characterized binding site and its molecular weight provide insights into PACAP's neuroendocrine signaling pathways.