Characteristics of non-opioid β-endorphin receptor

Tritium-labeled selective agonist of non-opioid beta-endorphin receptor, the decapeptide immunorphine ([H-3]SLT-CLVKGFY) with specific activity of 24 Ci/mmol has been prepared. By its use, non-opioid beta-endorphin receptors were revealed and characterized on mouse peritonea] macrophages and rat myocardium, spleen, adrenal, and brain membranes. The non-opioid beta-endorphin receptor of macrophages has in addition to immunorphine (K-d of the [H-3]immunorphine-receptor complex was 2.4 +/- 0.1 nM) and beta-endorphin (K-i of the [H-3]immunorphine specific binding was 2.9 +/- 0.2 nM) a high affinity for Fc-fragment of human IgGl, pentarphine (VKGFY), cyclopentarphine [cyclo(VKGFY)], and [Pro(3)]pentarphine (VKPFY) (K-i values were 0.0060 +/- 0.0004, 2.7 +/- 0.2, 2.6 +/- 0.2, and 2.8 +/- 0.2 nM, respectively) and is insensitive to naloxone and [Met(5)]enkephalin (K-i > 100 muM). Treatment of macrophages with trypsin resulted in the loss of their ability for the specific binding of [H-3]immunorphine. Values of the specific binding of 8.4 nM [H-3]immunorphine to rat adrenal, spleen, myocardium, and brain membranes were determined to be 1146.0 +/- 44.7, 698.6 +/- 28.1, 279.1 +/- 15.4, and 172.2 +/- 1.8 fmol/mg protein, respectively. Unlabeled beta-endorphin, pentarphine, [Pro(3)]pentarphine, cyclopentarphine, cyclodipentarphine [cyclo(VKGFYVKGFY)], and Fc-fragment of IgGl inhibited the binding of [H-3]immunorphine to membranes from these organs. No specific binding of [H-3]immunorphine to rat liver, lung, kidney, and intestine membranes was found.