Detection of a novel immunoreactive endomorphin 2-like peptide in rat brain extracts

Erzsébet Szemenyei, István Barna, Zsuzsa Mergl, Attila Keresztes, Zsuzsanna Darula, Erzsébet Kató, Géza Tóth, András Z. Rónai

Research output: Contribution to journalArticle

9 Citations (Scopus)


To pursue further the possible de novo biosynthetic pathway of endomorphins in rat brain we raised antibodies to endomorphin-2 conjugate in rabbits. Antiserum R1 recognized endomorphin-2 with good selectivity as compared to endomorphin-1 with a median detection value of 65.5 ± 7.5 pg/tube (n = 7), whereas R4 antiserum recognized both endomorphins with similar sensitivity. Neither antisera recognized YP-related di- or tripeptides or YGGF-related opioid sequences (enkephalins, β-endorphin, dynorphin). Using the same rat brain extraction-RP-HPLC-gradient separation paradigm as previously, antisera detected 144.6 ± 40.0 (n = 3) pg/g wet brain weight endomorphin-2-like immunoreactivity in the fraction corresponding to standard endomorphin-2 retention time and also in the fraction matching endomorphin-2-OH standard retention time (179.1 ± 30.1 pg/g). Since R1 failed to recognize authentic endomorphin-2-OH, the second immunoreactive species must be different from both endomorphin-2 and endomorphin-2-OH. Possible biosynthetic intermediates to endomorphins, synthetic YPFFG and YPWFG had retention times close to the parent endomorphin standards in RP-HPLC gradient separation profile. The former was a μ-opioid receptor agonist of medium potency in the in vitro assays (rat brain RBA&GTPγS binding and mouse vas deferens), whereas the latter was a weak μ-opioid receptor agonist with a significant δ-opioid receptorial action as well and a definite indication of partial agonism.

Original languageEnglish
Pages (from-to)54-61
Number of pages8
JournalRegulatory Peptides
Issue number1-3
Publication statusPublished - Jun 5 2008


  • Bioassays
  • Endomorphin
  • Novel endomorphin-2-immunoreactive species
  • Radioimmunoassay
  • Rat brain
  • [Gly]-endomorphins

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Endocrinology
  • Clinical Biochemistry
  • Cellular and Molecular Neuroscience

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