title: Experimental simulation of the environment of the delta opioid receptor. A 500 MHz study of enkephalins in CDCl3.
abstract: Complexes of [Met5] and [Leu5]enkephalin amides with 18-crown-6-ether have been studied in CDCl3 solution by means of 500 MHz NMR spectroscopy, in order to simulate two of the features of the opioid receptor: the apolar environment and the binding of the charged N atom. Contrary to all previous studies in polar solvents the NH resonances are spread in a huge range (ca. 4 ppm) as in the spectra of rigid cyclic peptides. The two observed intramolecular hydrogen bonds are consistent with the existence of a single, folded, conformation, i.e. a C10 beta-turn in which the Phe4 NH is linked to the Tyr1 CO group.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002725:Chloroform; D043844:Crown Ethers; D004735:Energy Transfer; D004745:Enkephalins / Q000378:metabolism*; D004988:Ethers, Cyclic; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation; D011522:Protons; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D012996:Solutions; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D043844:Crown Ethers; D004745:Enkephalins; D004988:Ethers, Cyclic; D011522:Protons; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D012996:Solutions; C015762:18-crown-6; D002725:Chloroform