Relative conformational rigidity in oxytocin and (1-penicillamine)-oxytocin: a proposal for the relationship of conformational flexibility to peptide hormone agonism and antagonism.

A comparative study of the proton and carbon-13 nuclear magnetic resonance spectral parameters of the peptide hormone oxytocin and of its competitive inhibitor [1-L-penicillamine]oxytocin has been made, and the results analyzed in terms of comparative conformational and dynamic properties. The results indicate that oxytocin has a flexible conformation, while [1-L-penicillamine]oxytocin has a more restricted conformation. The results provide a framework for understanding the mechanism of peptide hormone agonism and antagonism for these compounds, and an approach for understanding some features of the interaction of the hormone and related compounds with their receptor.

On the existence of a mono-vinyl d-urobilin.

Chromic acid degradation of a d-urobilin, obtained after incubation of bilirubin in fecal bacterial cultures, gave methylvinylmaleimide and methylethylmaleimide. The d-urobilin, molecular weight 588, C(33)H(40)-N(4)O(6), clearly showed the presence of both vinyl and ethyl resonances in the nuclear magnetic resonance spectrum. These results point unambiguously to a urobilin structure with one vinyl and one ethyl beta-substituent.

300-MHz nuclear magnetic resonance study of oxytocin aqueous solution: conformational implications.

The 300-MHz nuclear magnetic resonance spectrum of the peptide hormone, oxytocin, in water, was obtained. Extensive nuclear magnetic resonance spindecoupling experiments, including those involving irradiation of the alpha-proton resonance under the water peak, studies using partially deuterated hormone derivatives, and nuclear magnetic resonance studies of some precursor peptides to oxytocin, permitted us to assign most of the proton resonance of the hormone unambiguously. The JNalpha values and temperature dependence of the chemical shift of the peptide amide and carboxamide protons of oxytocin were also obtained. These studies indicate that, in aqueous solution, oxytocin is a flexible molecule possessing several different conformations. Corresponding studies of [4-leucine]oxytocin were also made, with similar results and conclusions.

Nuclear magnetic resonance spectrum of lysine-vasopressin in aqueous solution and its structural implictions.

The peaks in the proton NMR spectrum of lysine-vasopressin in aqueous solution at pH 3-5 were assigned to particular amino-acid residues by the use of the results of dilution studies and NH-C(alpha)H and C(alpha)H-C(beta)H decoupling experiments. The conformation of lysine-vasopressin in water differs from its conformation in dimethylsulfoxide.

Conformational studies on tocinamide and deaminotocinamide by 220 MHz nuclear magnetic resonance spectroscopy.

The 220 MHz spectra of tocinamide and deaminotocinamide, the ring moieties of oxytocin and of deamino-oxytocin, respectively, were investigated in [U-(2)H]dimethylsulfoxide solution. Extensive decoupling and exchange experiments allow complete spectral assignment and determination of many coupling constants. Circular dichroism spectra assigned a right-hand screw sense to the C-S-S-C group. The conformations of tocinamide and deaminotocinamide are different from each other and from those suggested for the ring portions of oxytocin and deamino-oxytocin. The relationship of this difference to biological activity is commented upon. The importance of the interaction of the side chain with the ring in oxytocin and deamino-oxytocin is emphasized.

Nuclear magnetic resonance studies of lysine-vasopressin: structural constraints.

The 220-MHz proton NMR spectra of lysine-vasopressin and some related compounds are examined in deuterated dimethyl sulfoxide to obtain structural information that must be satisfied by any proposed conformation of the molecule. This structural information is in the form of dihedral angles (for rotation about the NH-C(alpha)H bonds) from coupling constants, possible hydrogen bonding of the CONH(2) and backbone amide groups from the temperature-dependence of the chemical shift, and aromatic ring-aromatic ring interaction from the effect of the magnetically anisotropic groups on the chemical shift.

Conformation of cyclolinopeptide a observed by nuclear magnetic resonance spectroscopy.

The 220 MHz spectrum of the cyclic nonapeptide Phe-Phe-Leu-Ile-Ile-Leu-Val-Pro-Pro (all L), designated cyclolinopeptide A, is analyzed by decoupling, exchange of peptide NH protons with deuterium, and measurement of the temperature dependence of the NH chemical shift. Measurement of the NH doublet spacings gives values of J(Nalpha), the vicinal coupling of alpha-CH and NH protons of specific amino acid residues. These in turn provide estimates of the rotation angles [unk] about the HN-C(alpha)H(alpha) bonds, which in combination with energy minimization studies, allow the determination of the conformation of the main chain. It is concluded that this polypeptide in dimethylsulfoxide solution does not contain intramolecular hydrogen bonds. Deuterium-exchange rates and temperature-dependence studies indicate that of the seven peptide NH protons, five are exposed to solvent, while two, which exchange somewhat more slowly than the others, may be situated in the interior of the ring.

Nuclear magnetic resonance spectrum of lysine-vasopressin and its structural implications.

The NMR spectra at 220 MHz of lysinevasopressin and its precursors were measured in dimethyl sulfoxide, and the peaks were assigned to specific protons. Information about hydrogen bonding was obtained from the temperature coefficients of the chemical shifts. With these data, and with several chemical-shift positions and coupling constants, structural information was derived for this polypeptide hormone.

NMR studies on the conformation of derivatives of the side chain of oxytocin: examples of cis-trans isomerism.

The 220 MHz spectra reported in this paper show the existence of cis-trans isomerism about the Cys-Pro bond in (S-benzyl)-L-Cys-L-Pro-L-Leu-Gly(NH(2)) and about the Z-Pro bond in (N-benzyloxycarbonyl)-L-Pro-L-Leu-Gly(NH(2)). These peptides are derivatives of the side chain of oxytocin, which has the structure L-Pro-L-Leu-Gly(NH(2)). Taken in water-free (CD(3))(2)SO, the spectra also show differences between the two isomers in the amide chemical shifts, which indicate interaction of the terminal end of the peptides with the rest of the residues. The ratio of the isomeric forms is about 2:3 for the S-benzylcysteinyl peptide, while it is 1:1 for the N-benzyloxycarbonyl-protected peptide. The probable assignment of peaks in isomers is discussed, in addition to routine spectral assignments based on extensive decoupling experiments.