Interaction of the synthetic peptide octarphin with rat adrenal cortex membranes |
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Authors: | Y N Nekrasova Y A Zolotarev E V Navolotskaya |
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Institution: | 1. Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, pr. Nauki 6, 142290, Pushchino, Moscow Region, Russia 2. Institute of Molecular Genetics, Russian Academy of Sciences, pl. Kurchatova 2, 123182, Moscow, Russia
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Abstract: | The synthetic peptide octarphin (TPLVTLFK, fragment 12?C19 of ??-endorphin), a selective agonist of the nonopioid ??-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, Bmax1 = 41.0 ± 3.8 pmol/mg protein. The specific binding of 3H]octarphin to the membranes was inhibited by unlabeled ??-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, ??- and ??-endorphins, and corticotropin were inactive (K i > 1 ??M). 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 ??-endorphin receptor of adrenal cortex membranes. |
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