STABILIZATION OF THE PEPTIDE CONFORMATION ON THE MICELLAR SURFACE

The conformational mobility of peptide molecules plays a significant r ole in peptide-receptor interactions and quantitative structure-activi ty relationships. As a receptor mimetic system, bis(2-ethylhexyl) sodi um succinate (AOT) reversed micelles containing an aqueous solution of one of the melanotrophine inhibiting factor analogues prolyl- tyrosyl -glycinamide hydrochloride in the inner cavity have been used. Two-dim ensional nuclear magnetic resonance spectroscopy (NOESY) and C-13 spin -lattice relaxation time measurements have been used to establish that the peptide molecule assumes the biologically active beta(II) turn co nformation when it is adsorbed at the surfactant-water border. This co nformation is stabilized by intramolecular H-bonding between the proli ne carbonyl oxygen atom and amide protons. Moreover, it has been shown that the phenyl ring of tyrosine was inserted into the AOT intermolec ular cavity, which is located between the polar AOT groups and the bra nches of iso-octane fragments. By and large, the phenyl ring acts as a hydrophobic anchor. Reversed micelles can be regarded as providing a realistic model of the receptor.