The peptide T345-359 representing the fourth intracellular loop of the avian beta-adrenoceptor has been shown to strongly inhibit receptor-mediated adenylate cyclase activity [Münch, G., Dees, C., Hekman, M., & Palm, D. (1991) Eur. J. Biochem. 198, 357-364]. Circular dichroism and two-dimensional 1H NMR techniques were used to investigate the three-dimensional structure of the peptide in trifluoroethanol, phospholipid micelles, and small unilamellar phospholipid vesicles. The prepared vesicles were tested for size distribution and stability by using electron microscopy, photon correlation spectroscopy, and 31P NMR spectroscopy. The peptide T345-359 adopted a predominantly alpha-helical conformation in either trifluoroethanol or phospholipid micelles and vesicles. No structural differences were found for the conformation of the peptide in the presence of phospholipid micelles or vesicles, respectively, using 2D 1H NMR techniques, suggesting a unique conformation of T345-359 when associated with model membranes. A computer-aided model of the micelle-associated peptide was derived. The relevance of the 3D structure of the intracellular loops of receptors to communicate with the G protein in the signal transduction cascade is discussed.

We have investigated the structure of synthetic peptides corresponding to residues 284-295 of the turkey erythrocyte adrenoceptor in micelles, trifluoroethanol and aqueous solution, by using 2D IH NMR and CD. In the presence of phospholipid micelles the peptides display a C-terminal a-helical region, whereas the N-terminal part was found to be highly flexible.

Astrocytoma (WHO grade II, III), glioblastoma, malignant melanoma, and normal glial cell cultures, established from biopsies, were investigated by 1H MRS. At a 1H resonance frequency of 500 MHz (11.75 T) a high spectral resolution was achieved in 1D 1H spectra; in conjunction with 2D shift-correlated (COSY) MRS, resonances of alanine, aspartate, choline, creatine, glutamate, glutamine, hypotaurine, myo-inositol, phosphocreatine, phosphoryl-ethanolamine, phosphoryl-choline, lactate, lysine, N-acetylaspartate, taurine, threonine and valine could be identified. T1 relaxation times for the most prominent compounds are presented. T1 values of lactate ranged between 450 ms and 850 ms. The intensity of the lactate signal revealed differences between individual spectra, but exhibited no correlation between different tumor specimens or degree of malignancy. It was shown that the lactate signal at 1.3 ppm is covered by peaks arising from threonine and fatty acids. The choline signal level varied among spectra of different tumors, among tumors with similar degree of malignancy, and within the same tumor. Further preliminary differences due to aspartate, inositol and glutamine/glutamate were found in 1D and 2D COSY spectra between normal glial cells as well as different tumors. These results indicate that some differences observed in in vivo spectra may be attributable to secondary macroscopic structural changes (hypoxia, necrosis) and not to tumor inherent characteristics. Further correlation between in vivo and in vitro spectroscopy is therefore required.