Binding of synthetic peptide TPLVTLFK to nonopioid beta-endorphin receptor on rat brain membranes

The synthetic peptide TPLVTLFK corresponding to the sequence 12-19 of beta-endorphin (referred to as octarphin) was found to bind to high-affinity naloxone-insensitive binding sites on membranes isolated from the rat brain cortex (K-d = 2.6 +/- 0.2 nm). The binding specificity study revealed that these binding sites were insensitive not only to naloxone but also to alpha-endorphin, gamma-endorphin, [Met(5)]enkephalin, and [Leu(5)]enkephalin, as well. The [H-3]octarphin specific binding with brain membranes was inhibited by unlabeled beta-endorphin (K-i = 2.4 +/- 0.2 nm) and a selective agonist of nonopioid beta-endorphin receptor decapeptide immunorphin SLTCLVKGFY (K-i = 2.9 +/- 0.2 nm). At the same time, unlabeled octarphin completely (by 100%) inhibited the specific binding of [H-3]immunorphin with membranes (K-i = 2.8 +/- 0.2 nm). Thus, octarphin binds with a high affinity and specificity to nonopioid receptor of beta-endorphin on rat brain cortex membranes. Copyright (C) 2010 European Peptide Society and John Wiley & Sons, Ltd.