Interactions of Tyr-MIF-1 at opiate receptor sites.
Binding of Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) to mu and delta opiate receptors was compared with other putative opiate antagonist peptides by displacement of iodinated ligands selective for mu (DAGO, FK33824, and morphiceptin) and delta (DPDPE) receptors. Tyr-MIF-1 and ACTH (1-24 and 1-39) inhibited binding of 125I-DAGO with IC50's of about 1 microM. FMRF-NH2 was about an order of magnitude weaker while CCK-8 and MIF-1 failed to inhibit 50% of binding at concentrations up to 100 microM. Morphiceptin, Tyr-MIF-1, and ACTH were less potent but more efficacious than DAGO, FK33824, morphine, or naloxone in inhibiting the binding of 125I-morphiceptin. Tyr-MIF-1 appeared to have a more selective action at opiate receptors than ACTH; in contrast to their effects at 125I-DAGO-labeled sites, morphiceptin and Tyr-MIF-1 inhibited less than 50% of 125I-DPDPE binding at concentrations up to 10 and 50 microM, while ACTH 1-39 and 1-24 inhibited more than 80% of the binding at 2.5 and 5 microM, respectively. The results indicate that at relatively high concentrations Tyr-MIF-1, like ACTH, can affect binding to the opiate receptor, but unlike ACTH, binding of Tyr-MIF-1 appears relatively selective for the mu site.
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D004723:Endorphins / Q000378:metabolism; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000378:metabolism; D066298:In Vitro Techniques; D009075:MSH Release-Inhibiting Hormone / Q000031:analogs & derivatives* / Q000378:metabolism; D008297:Male; D009270:Naloxone / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu
D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; C036930:tyrosyl-prolyl-leucyl-glycinamide; D020881:Enkephalin, D-Penicillamine (2,5)-; D009075:MSH Release-Inhibiting Hormone; C028889:morphiceptin