Interaction of synthetic peptide octarphin with human blood lymphocytes

The synthetic peptide octarphin (TPLVTLFK, fragment 12-19 of β-endorphin), a selective agonist of nonopioid β-endorphin receptor, was prepared with specific activity 28 Ci/mmol. The binding of [3H]octarphin to T and B lymphocytes isolated from the blood of donors was studied. It was found that [3H]octarphin binds both to T and B cells with high affinity: Kd = 3.0 ± 0.2 and 3.2 ± 0.3 nM, respectively. The specific binding of [3H]octarphin to T and B lymphocytes was competitively inhibited by unlabeled β-endorphin (Ki = 1.9 ± 0.2 and 2.2 ± 0.3 nM, respectively) and was not inhibited by unlabeled naloxone, [Met(5)]enkephalin, [Leu(5)]enkephalin, α-endorphin, and γ-endorphin. Thus, T and B lymphocytes of human blood possess a nonopioid β-endorphin receptor whose binding is provided by the fragment 12-19 (the octarphin sequence).