The Use of Tritium-Labeled Dermorphin for Studying the Interactions of C-Terminal Dermorphin Fragment Tyr-Pro-Ser-NH_2 and Its Stereoisomer Tyr-D-Pro-Ser-NH_2 with Opioid Receptors

摘要

Two sites for binding dermorphin to the membrane receptors have been discovered in the rat brain (1.5-3 and >5 nM). The binding constants and receptors concentrations for the first and second sites are the following: K_D = 0.26 +- 0.07 nM; fimax = 24+- 0.66 fmol/mg protein and K_D = 1.7 +- 0.01 nM; Bmax = 53 +- 4.4 fmoVmg protein, respectively. As determined by radioreceptor assay, the C-end fragment of dermorphin, Tyr-Pro-Ser-NH_2, and its Stereoisomer Tyr-D-Pro-Ser-NH_2, replaced [3H]-dermorphin from rat brain opioid receptors, (EC_50: 7.8 +- 2.5 mu M and 5 +- 1.5 mu M). Note that tripeptides replaced dermorphin only from the "high-affinity" binding sites (1.5-3 nM).