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Biomedical subjects

R Deslauriers

Publications and source records attributed to R Deslauriers.

At least 127 records · Page 7Linked to original sources
PubMed1975

Conformational flexibility of luteinizing hormone-releasing hormone in aqueous solution. A carbon-13 spin-lattice relaxation time study.

The carbon-13 nuclear magnetic resonance (13C NMR) spectra of luteinizing hormone-releasing hormone (LH-RH) and lower homologous peptides have been assigned in aqueous solutions at various pH values. 13C spin-lattice relaxation times (T1) have been measured for all proton-bearing carbons at 25.2 and 67.9 MHz. From the T1 data the rates of overall molecular motion and intramolecular motion of side chains have been estimated. LH-RH is a flexible molecule in solution, having segmental motion along the backbone as well as in the nonaromatic side chains.

Chemical Phenomena↗
PubMed1975

Conformational flexibility of angiotensin II. A carbon-13 spin-lattice relaxation study.

Carbon-13 spin-lattice relaxation times (T1) have been determined for the carbon in the octapeptide hormone [5-isoleucine]-angiotensin II in aqueous solution. Two possible models for molecular motion are considered: isotropic overall motion of the hormone with internal motion of some residues and anisotropic overall molecular motion. The data are interpreted in detail using the former model. The alpha carbons of the peptide backbone are all equally restricted in their motion. The correlation time for overall molecular reorientation, calculated from an everage T1 value of 95 msec for the alpha carbons in the peptide backbone, is ca. 5 times 10-10 sec. The carbons in the side chains are more mobile than those in the peptide backbone, with the exception of the side chain of the Tyr residue which does not undergo rapid segmental motion. We propose that [5-isoleucine]-angiotensin II has a restricted backbone conformation and that the alpha carbons of the N- and C-terminal residues are constrained to nearly the same extent as the remaining alpha carbons in the peptide backbone. Chemical shift data indicate that the Pro residue adopts the trans conformation about the His-Pro bond and that the imidazole ring of His has a strong preference for the N-tau -H tautomer.

Amino Acid Sequence↗
PubMed1974

Long-range, pH-dependent effects on the carbon-13 nuclear magnetic resonance spectra of oxytocin.

The effects of hydrogen ion concentrations on the carbon-13 nuclear magnetic resonance spectra of oxytocin were investigated. The starting pD of 3.0 was increased stepwise to 8.4. A change of the state of protonation of the N-terminal amino group of oxytocin is accompanied by changes in chemical shifts of carbon-13 nuclei of amino-acid residues located in the 20-membered ring of the hormone. The resonance positions of the acyclic peptide portion, Pro-Leu-Gly-NH(2), remain constant. The pD-induced chemical-shift changes of carbons up to five bonds removed from the site of protonation are interpreted in terms of "through-bond" and "through-space" mechanisms. Chemical-shift changes of carbons more than five bonds removed are proposed to have a conformational origin. It is suggested that a change in the charge density of the amino group perturbs the dihedral angle of the -CH(2)-S-S-CH(2)- moiety of oxytocin, which in turn significantly affects the overall conformation of the 20-membered ring of the hormone.

Carbon Isotopes↗
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↗