Characterization of zeta (ζ): a new opioid receptor involved in growth

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Endogenous opioid systems (i.e., opioids and opioid receptors) are known to play a role in neural cancer. Using [3H]-[Met5]enkephalin, a potent ligand involved in growth, specific and saturable binding was detected in homogenates of S20Y neuroblastoma transplanted into A/Jax mice; the data fit a single binding site. Scatchard analysis yielded a Kd of 0.49 nM and a binding capacity of 5.32 fmol/mg protein. Binding was dependent on protein concentration, time, temperature, and pH, and was sensitive to Na+ and guanine nucleotides. Optimal binding required protease inhibitors, and pretreatment of the tumor homogenates with trypsin markedly reduced [3H]-[Met5]enkephalin binding, suggesting that the binding site was proteinaceous in character. Displacement experiments indicated that [Met5]enkephalin was the most potent displacer of [3H]-[Met5]enkephalin; other ligands selective for μ, δ, κ, ε, and σ were not highly competitive. Given the functional significance of [Met5]enkephalin as a potent regulator of normal and abnormal growth, and that the receptor recognized by [Met5]enkephalin does not resemble any previously described, the present study has demonstrated the presence of a new opioid receptor termed zeta (ζ) (from the Greek 'Zoe', life) related to the proliferation of cells and tissues.

Original languageEnglish (US)
Pages (from-to)297-305
Number of pages9
JournalBrain research
Issue number2
StatePublished - Mar 20 1989

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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