Interaction of the Synthetic Peptide Octarphin with Rat Adrenal Cortex Membranes

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Y. N. Nekrasova¹, Y. A. Zolotarev², and E. V. Navolotskaya^1*

¹Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, pr. Nauki 6, 142290 Pushchino, Moscow Region, Russia; fax: (4967) 33-0527; E-mail: navolotskaya@fibkh.serpukhov.su; elenanavolots@gmail.com

²Institute of Molecular Genetics, Russian Academy of Sciences, pl. Kurchatova 2, 123182 Moscow, Russia; fax: (495) 196-0221

^* To whom correspondence should be addressed.

Received May 17, 2012; Revision received June 1, 2012

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The synthetic peptide octarphin (TPLVTLFK, fragment 12-19 of β-endorphin), a selective agonist of the non-opioid β-endorphin receptor, was labeled with tritium yielding specific activity of 28 Ci/mmol. The binding of [³H]octarphin to rat adrenal cortex membranes was studied under normal conditions as well as after cold and heat shocks. It was found that under normal conditions [³H]octarphin specifically binds to the membranes with high affinity: K_d1 = 36.3 ± 2.5 nM, B_max1 = 41.0 ± 3.8 pmol/mg protein. The specific binding of [³H]octarphin to the membranes was inhibited by unlabeled β-endorphin (K_i = 33.9 ± 3.6 nM) and the agonist of the non-opioid receptor decapeptide immunorphin (K_i = 36.8 ± 3.3 nM). Unlabeled naloxone, [Leu⁵]- and [Met⁵]enkephalins, a- and γ-endorphins, and corticotropin were inactive (K_i > 1 µM). Both cold and heat shocks decreased the binding affinity: K_d2 = 55.6 ± 4.2 nM and K_d3 = 122.7 ± 5.6 nM, respectively. In both cases, the maximal binding capacity of the receptor did not change. Thus, even a short-term thermal shock significantly affects the sensitivity of the non-opioid β-endorphin receptor of adrenal cortex membranes.

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KEY WORDS: β-endorphin, naloxone, peptides, receptors, adrenal cortex

DOI: 10.1134/S000629791212005X

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