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Morphine enhances the phosphorylation of a 58 kDa protein in mouse brain membranes
K Nagamatsu1, K Suzuki, R Teshima
1National Institute of Hygienic Sciences, Tokyo, Japan.
Abstract:
Morphine and [D-Ala2,D-Leu5]enkephalinamide enhance the phosphorylation of a 58 kDa protein in mouse brain synaptosomal membranes. The enhancement of phosphorylation was inhibited by naloxone, an antagonist of morphine. The phosphorylated 58 kDa protein was retained on wheat-germ-agglutinin-agarose and morphinone-Affi-Gel 401 columns and biospecifically eluted out from the columns with N-acetyl-D-glucosamine and naloxone respectively. These results suggest a strong possibility that the opiate-binding protein undergoes phosphorylation by endogenous protein kinase. Since the molecular mass of a mu-type opioid receptor in mouse brain is suggested to be 58 kDa, coincident with those of rat brain and neuroblastoma x glioma hybrid cells, it is conceivable that the phosphorylated 58 kDa protein is a mu-type receptor.
Insights
Morphine and enkephalinamide increase the phosphorylation of a 58 kDa protein in mouse brain membranes. This suggests the mu-type opioid receptor may be phosphorylated by an endogenous protein kinase.
Area of Science:
- Neuroscience
- Molecular Biology
- Pharmacology
Background:
- Opioid receptors are crucial targets for pain management.
- Understanding opioid receptor signaling pathways is essential for developing novel therapeutics.
Purpose of the Study:
- To investigate the effect of opioid agonists on protein phosphorylation in mouse brain synaptosomal membranes.
- To identify the phosphorylated protein and its potential role in opioid receptor function.
Main Methods:
- Incubation of mouse brain synaptosomal membranes with morphine and [D-Ala2,D-Leu5]enkephalinamide.
- Inhibition studies using naloxone, a known opioid antagonist.
- Affinity chromatography using wheat-germ-agglutinin-agarose and morphinone-Affi-Gel 401 columns.
- Biospecific elution with N-acetyl-D-glucosamine and naloxone.
Main Results:
- Morphine and [D-Ala2,D-Leu5]enkephalinamide significantly enhanced the phosphorylation of a 58 kDa protein.
- Naloxone inhibited this enhancement, indicating an opioid-specific mechanism.
- The phosphorylated 58 kDa protein was purified using affinity chromatography.
- The protein was biospecifically eluted by N-acetyl-D-glucosamine and naloxone.
Conclusions:
- The findings strongly suggest that the opiate-binding protein undergoes phosphorylation by an endogenous protein kinase.
- The 58 kDa molecular mass aligns with known mu-type opioid receptors in various tissues.
- It is conceivable that the phosphorylated 58 kDa protein represents the mu-type opioid receptor.