Elsevier

Developmental Brain Research

Volume 45, Issue 2, 1 February 1989, Pages 283-289
Developmental Brain Research

Research report
Cross-linking of [125I]β-endorphin to μ-opioid receptors during development

https://doi.org/10.1016/0165-3806(89)90046-1Get rights and content

Abstract

Radioiodinated human β-endorphin was cross-linked to opioid receptors from rat brain membranes using the bifunctional reagents bis-[2-(succinimidooxycarbonyloxy)ethyl] sulfone (BSCOES) and disuccinimidyl suberate (DSS). Major radiolabeled bands migrated with Mr values of 65,000, 55,000 and 33,000, however the presence of the 55 kDa band was variable. The 65 kDa band was characterized as the μ-receptor: the binding of [125I]β-endorphin to this band was displaced by μ-selective ligands and blocked by alkylation of the receptor by μ-specific, but not δ-specific alkylating agents.

The cross-linked receptor underwent alterations in mol. wt. during development. Early in development, embryonic day 18 and postnatal day 1, the [125I]β-endorphin-labeled material migrated as a single band of mol. wt. 55 kDa. By day 21 postnatally the higher mol. wt. band of 65 kDa was present, as was material of 53, 47 and 43 kDa. Although the protein labeled early in development migrated with a mol. wt. of 55 kDa similar to the δ-receptor isolated from NG108-15 neuroblastoma-glioma cells, competition studies suggest this protein is not the δ-receptor. The 65 kDa band, tentatively identified as the μ-receptor, was present in adults but not detected in neonates, despite competition binding data indicating the presence of μ-sites. The results suggest that the 55 kDa band found in the 1-day-old neonate may be an immature form of the μ-opioid receptor that undergoes posttranslational modification, perhaps glycosylation, during development.

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