Interaction of synthetic peptide octarphin (TPLVTLFK) with human blood lymphocytes

The synthetic peptide octarphin (TPLVTLFK) corresponding to the sequence 12–19 of β‐endorphin, a selective agonist of non‐opioid β‐endorphin receptor, was labeled with tritium to specific activity of 29 Ci/mmol. The analysis of [³H]octarphin binding to human T and B lymphocytes separated from normal human blood revealed the existence of one type of high‐affinity binding sites (receptors): K_d 3.0 and 3.2 nM, respectively. Besides unlabeled octarphin, unlabeled β‐endorphin possessed the ability to inhibit the specific binding of [³H]octarphin to Т and B lymphocytes (K_i 1.9 and 2.2 nМ, respectively). Tests of the specificity of the receptors revealed that they are not sensitive to naloxone, α‐endorphin, γ‐endorphin, [Met⁵]enkephalin, and [Leu⁵]enkephalin. Thus, both T and B lymphocytes from normal human blood express non‐opioid receptor for β‐endorphin. Binding of the hormone to the receptor provides a fragment 12–19. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.