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 [(3) H]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): Kd 3.0 and 3.2 nM, respectively. Besides unlabeled octarphin, unlabeled β-endorphin possessed the ability to inhibit the specific binding of [(3) H]octarphin to Т and B lymphocytes (Ki 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, [Met(5) ]enkephalin, and [Leu(5) ]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.