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Stereospecific opiate-binding sites occur in coated vesicles
Summary
Researchers purified clathrin-coated vesicles from bovine brain and found they contain specific opioid-binding sites. These purified vesicles exhibit characteristic opioid binding properties, suggesting a role in opioid signaling.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Clathrin-coated vesicles are crucial for intracellular trafficking.
- The presence and function of opioid receptors in these vesicles are not fully understood.
Purpose of the Study:
- To purify clathrin-coated vesicles from bovine brain.
- To investigate the presence and characteristics of opioid-binding sites within these purified vesicles.
Main Methods:
- Sucrose or deuterium oxide-Ficoll density gradient centrifugation and permeation chromatography were used for purification.
- Electron microscopy (EM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were employed for homogeneity assessment.
- Binding assays were performed using tritiated naltrexone and etorphine.
Main Results:
- Purified fractions were enriched in clathrin-coated vesicles (up to 98%) and characteristic protein bands (180,000, 100,000, 50,000, and 35,000 daltons).
- Specific binding of naltrexone and etorphine to coated vesicles was demonstrated, with significant enrichment after purification steps.
- Naltrexone binding was stereospecific, and both ligand bindings were inhibited by guanyl-5'-yl imidodiphosphate and NaCl, indicating opioid receptor-like properties.
Conclusions:
- Purified bovine brain clathrin-coated vesicles possess high-affinity, stereospecific opiate alkaloid-binding sites.
- These binding sites display properties consistent with opioid receptors.
- The findings suggest a potential role for clathrin-coated vesicles in opioid signaling pathways within the brain.