Pharmacology of a new tritiated endomorphin-2 analog containing the proline mimetic cis-2-aminocyclohexanecarboxylic acid

Attila Keresztes, Erika Birkás, Annamária Páhi, Géza Tóth, Lidia Bakota, Károly Gulya, Mária Szücs

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8 Citations (Scopus)


As part of ongoing work aimed at generating proteolytically stable, readily applicable, radiolabeled endomorphin-2 (EM-2) analogs for elucidation of the topological requirements of peptide binding to μ-opioid receptors, we report here on the synthesis, radiolabeling, binding kinetics and binding site distribution of an EM-2 analog in which Pro2 is replaced by 2-aminocyclohexanecarboxylic acid, ACHC. [3H][(1S,2R)ACHC] 2EM-2 (specific activity 63.49 Ci × mmol-1) bound specifically to its binding sites with high affinity (KD = 0.55 ± 0.06 nM) and saturably, yielding a receptor density, Bmax of 151 ± 4 fmol × mg protein-1 in rat brain membranes. A similar affinity value was obtained in kinetic assays. Both Na+ and Gpp(NH)p decreased the affinity, proving the agonist character of the radioligand. Specific μ-opioid ligands displaced the radioligand with much higher affinities than did δ- and κ-ligands. The autoradiographic distribution of the binding sites of [3H][(1S,2R)ACHC] 2EM-2 agreed well with the known locations of the μ-opioid receptors in the rat brain. In consequence of its high affinity, selectivity and enzymatic resistance [19], the new radioligand will be a good tool in studies of the topographical requirements of μ-opioid-specific peptide binding.

Original languageEnglish
Pages (from-to)722-728
Number of pages7
Issue number4
Publication statusPublished - Apr 1 2011



  • 2-Aminocylcohexanecarboxylic acid (ACHC)
  • Autoradiography
  • Endomorphin
  • Peptide synthesis
  • Proteolytic stability
  • Radiolabeling
  • Receptor binding

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Endocrinology
  • Cellular and Molecular Neuroscience

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