PubMed Health⌕ Search

Biomedical subjects

R Walter

Publications and source records attributed to R Walter.

At least 253 records · Page 14Linked to original sources
PubMed1974

Tertiary structure of H-Pro-Leu-Gly-NH2, the factor that inhibits release of melanocyte stimulating hormone, derived by conformational energy calculations.

Conformational energy calculations were carried out on H-Pro-Leu-Gly-NH(2), the factor that inhibits the release of melanocyte stimulating hormone, and its biologically active analog, H-Pro-Ala-Gly-NH(2). Both peptides were found to be relatively compact molecules that retain, however, some degree of flexibility. After structure refinement, H-Pro-Leu-Gly-NH(2) possesses at least three preferred compact conformations. Two of these conformations occupy rather broad and flat energy troughs, while a third occupies a narrow and deep potential energy well. This third structure, which consists of a 10-membered beta-turn closed by a (4 --> 1) hydrogen bond between the proton of the trans carboxamide of Gly and the C=O of Pro, is the one that was proposed for H-Pro-Leu-Gly-NH(2) in dimethylsulfoxide and was also found by x-ray analysis.

Melanocyte-Stimulating Hormones↗
PubMed1973

Proton magnetic resonance study of peptide conformation: effect of trifluoroethanol on oxytocin and 8-lysine-vasopressin.

The usefulness of 2,2,2-trifluoroethanol titration as a means of distinguishing between intramolecular peptide-peptide hydrogen bonding on the one hand and intermolecular peptide-peptide and peptide-solvent hydrogen bonding on the other has been investigated with neurohypophyseal hormones, and the results have been compared with those of other methods. The chemical shifts (220 MHz) of the resonances of amide NH and aromatic CH protons of oxytocin, lysine vasopressin, deamino-lysine vasopressin, and deamino-8-tosyllysine vasopressin were monitored as the solvent composition was progressively varied from 100% dimethylsulfoxide to 100% 2,2,2-trifluoroethanol. The overall backbone conformation of oxytocin appears to be retained, and possibly somewhat stabilized, during the solvent transition, while the backbone, particularly the acyclic component, of lysine vasopressin and its analogs is subject to solvent-induced perturbation.

Ethanol↗
PubMed1973

Conformational studies of oxytocin, lysine vasopressin, arginine vasopressin, and arginine vasotocin by carbon-13 nuclear magnetic resonance spectroscopy.

Oxytocin, arginine vasopressin, lysine vasopressin, arginine vasotocin, as well as their cyclic and acyclic analogs, were studied by carbon-13 nuclear magnetic resonance spectroscopy in deuterium oxide and deuterated dimethylsulfoxide. Fourier-transformed spectra were obtained at 25.16 MHz. The resonances of all carbon atoms have been assigned in both solvent systems; this includes tentative assignments of the carbonyl carbons. The spectra of arginine vasopressin and lysine vasopressin are essentially identical when compared in D(2)O or dimethylsulfoxide, but they differ from those of oxytocin. The spectrum of arginine vasotocin in D(2)O is intermediate between those of oxytocin and the vasopressins. These spectral differences are not only due to variations in constituent amino acids but are also a reflection of conformational differences of oxytocin, arginine vasotocin, and the vasopressins. All hormones are sensitive to changes in hydrogen ion concentration in both solvents; this was not observed with deamino analogs, which lack the terminal amino group.

Arginine↗