Synthesis, radiolabeling and receptor binding of [3H][(1S,2R)ACPC2]endomorphin-2

Attila Keresztes, Géza Tóth, Ferenc Fülöp, Mária Szucs

Research output: Contribution to journalArticle

8 Citations (Scopus)


Previously, we have shown that substitution of Pro2 for cis-2-aminocyclopentanecarboxylic acid, ACPC in endomorphin-2 results in an analogue with greatly augmented proteolytic stability, high μ-opioid receptor affinity and selectivity. We now report the synthesis and biochemical characterization of [3H][(1S,2R)ACPC2]endomorphin-2 with a specific activity of 1.41 TBq/mmol (38.17 Ci/mmol). Specific binding of [3H][(1S,2R)ACPC2]endomorphin-2 was saturable and of high affinity with an equilibrium dissociation constant, Kd = 1.80 ± 0.21 nM and receptor density, Bmax = 345 ± 27 fmol × mg protein-1 at 25 °C in rat brain membranes. Similar affinity values were obtained in kinetic and displacement assays. Both Na+ and Gpp(NH)p decreased the affinity proving the agonist character of the radioligand. [3H][(1S,2R)ACPC2]endomorphin-2 retained the μ-specificity of the parent peptide. The new radioligand will be a useful tool to map the topographical requirements of μ-opioid peptide binding due to its high affinity, selectivity and enzymatic stability.

Original languageEnglish
Pages (from-to)3315-3321
Number of pages7
Issue number12
Publication statusPublished - Dec 1 2006



  • 2-Aminocylcopentanecarboxylic acid
  • Conformational constrain
  • Endomorphin
  • Radiolabeling
  • Receptor binding

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Endocrinology
  • Cellular and Molecular Neuroscience

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