Endomorphin-1 (Tyr-Pro-Trp-Phe-NH 2 ) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH 2 ), peptides recently isolated from bovine and human brain, have high affinity and selectivity for μ opiate receptors. They share sequence similarity with the endogenous opiate-modulating peptide Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH 2 ). The efficacies of these endogenous peptides and of the enkephalin analog DAMGO were compared by measuring their effects on the binding of guanosine-5′- O -(γ-( 35 S)thio)triphosphate (( 35 S)GTPγS) to G-proteins in membranes from SH-SY5Y human neuroblastoma cells. DAMGO, endomorphin-1, and endomorphin-2 stimulated ( 35 S)GTPγS binding dose dependently, with maximal effects of 60 ± 9%, 47 ± 9%, and 43 ± 6% stimulation above basal and ED 50 of 49 ± 8 n M , 38 ± 8 n M , and 64 ± 13 n M , respectively. Tyr-W-MIF-1 showed only a small stimulation of binding (5% stimulation above basal, ED 50 = 2 μ M ). When given in combination with the other opioids, however, Tyr-W-MIF-1 attenuated their ability to activate G-proteins. Thus, the endogenous opioids endomorphin-1 and endomorphin-2 activate G-proteins similarly to the synthetic agonist DAMGO, but the structurally similar peptide Tyr-W-MIF-1 produces only minimal stimulation of G-proteins.
Peptides – Elsevier
Published: Apr 1, 1998
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