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Biomedical subjects

J Kobayashi

Publications and source records attributed to J Kobayashi.

At least 523 records · Page 29Linked to original sources
PubMed1981

Nuclear magnetic resonance study on solvent dependence of side chain conformations of tyrosine and tryptophan derivatives.

The stereoselectively beta-deuterated species of Ac-Ar-NHMe, Ac-Ar-OH and Ac-Ar-OEt (Ar = Tyr and Trp) and H-Trp-NHMe were synthesized. 270-MHz 1H n.m.r. spectra of the normal and deuterated species of these aromatic amino acid derivatives were analyzed. For most of the tyrosine and tryptophan derivatives in various polar and nonpolar solvents, the lower-field and higher-field beta-proton signals were found to be due to the pro-S and pro-R protons, respectively. However, the alternative assignments apply for H-Trp-NHMe in aqueous solution and for Ac-Tyr-NHMe and Ac-Trp-NHMe in nonpolar solvents. Such alternative assignments of beta-proton signals were also found for H-Phe-NHMe, Ac-PHe-NMe2 and Ac-Phe-OtBu. From the analyses of the 1H n.m.r. spectra of tyrosine and tryptophan derivatives, the vicinal coupling constants and rotamer populations about the C alpha-C beta bond were determined in various solvents. The rotamer populations of H-Trp-NHMe, Ac-Ar-NHMe, Ac-Ar-OH and Ac-Ar-OEt depend significantly on solvent polarity. Each of these four types of derivatives exhibits specific solvent-polarity dependences of rotamer populations. The solvent dependences of rotamer populations were substantially reduced on replacement of alpha-carbonyl group by methylene group, suggesting the effect of this carbonyl group in the solvent dependence of rotamer populations.

Magnetic Resonance Spectroscopy↗
PubMed1981

Biphasic mechanical responses of the guinea-pig isolated ileum to the venom of the marine snail Conus striatus.

Venom extract of Conus striatus elicited a rhythmic, transient contraction of the guinea-pig isolated ileum followed by a relaxation at concentrations greater than 1 microgram/ml, which was abolished by tetrodotoxin and a low-Na medium. The contraction induced by the venom was inhibited by atropine but not mecamylamine, whereas the relaxation was not affected by bretylium, guanethidine or phentolamine. These results suggest that the contraction of the ileum induced by the venom is due to the excitation of cholinergic nerves, while the relaxation is mediated through non-adrenergic inhibitory nerves.

Animals↗
PubMed1980

Nuclear magnetic resonance study of side-chain conformation of tyrosyl residue in [Met5]-enkephalin. Solvent and temperature dependence.

[Met5]-Enkephalin and tyrosine methylamide containing (2S, 3S)-[2,3-2H]-tyrosine and [Met5]-enkephalin containing (2S, 3R)-[3-2H]tyrosine were synthesized. 270 MHz 1H-NMR spectra of the normal species and selectively deuterated species were analyzed. The lower field and higher field beta-proton signals of the Tyr1 residues of [Met5]-enkephalin (and tyrosine methylamide) were unambiguously assigned to the pro-S and pro-R protons, respectively, in organic solvents, but the alternative assignments apply in 1H2O. For [Met5]-enkephalin and tyrosine methylamide (model for N-terminal tyrosyl residue), the rotamer populations around the Calpha-Cbeta bond of tyrosyl residue were determined in a variety of solvents. Rotamer populations of the tyrosyl residue depend on solvent polarity. In aqueous solution, the rotamers I and II are predominant while in weakly polar solvents the rotamer I becomes predominant. For the tyrosyl residue of the dipolar form of [Met5]-enkephalin in (C2H3)2SO solution, anomalous temperature dependences of rotamer populations are observed. This anomaly is suggested to be due to the equilibrium of the folded and extended conformations of the main chain. In fact, the temperature dependences of rotamer populations become normal in the presence of 2 M NH4ClO4, which weakens the attraction between the N-terminal and C-terminal groups of the dipolar form and thus reduces the population of the folded form in (C2H3)2SO solution.

Dimethyl Sulfoxide↗
PubMed1980

Tardive dyskinesia and institutional practice: current issues and guidelines.

Despite increasing public and legal pressures to minimize the occurrence of tardive dyskinesia, the practicing clinician often feels there are no alternatives to the use of neuroleptic medication in the treatment of psychosis. However, there are many clinical situations in which the use of neuroleptics may be avoided; guidelines for such situations, including the treatment of affective disorders and of chronic schizophrenia, are presented. The authors also discuss the use of alternative treatment programs and psychosocial interventions that may allow significant reduction in neuroleptics, and they describe new areas of research aimed at preventing and treating tardive dyskinesia.

Affective Symptoms↗
PubMed1979

Nuclear magnetic resonance study of side-chain conformation of phenylalanine residue in [Met5]-enkephalin: solvent, pH, and temperature dependence.

[Met5]-Enkephalin and N-acetylphenylalanine methylamide containing (2S,3S)-[2,3-2H2]Phe were synthesized 270 MHz 1H NMR spectra of the normal and selectively deuterated species were analysed. The lower-field and higher-field beta-proton signals of the Phe4 residue of [Met5]-enkephalin were unambiguously assigned to the pro-S and pro-R protons, respectively. The same assignments apply to N-acetylphenylalanine methylamide in polar organic solvents and in 2H2O, but the alternative assignments apply in C2HCl3. For [Met5]-enkephalin, the vicinal spin coupling constants 3JalphabetaS and 3 JalphabetaR and the rotamer populations around the Calpha-Cbeta bond were determined in a variety of solvents. From the pH and temperature dependences of rotamer populations of [Met5]-enkephalin, the side-chain conformation of the Phe residue in 2H2O solution was found to be considerably different from that in (C2H3)2SO solution. Rotamer populations of the Phe4 residue of [Met5]-enkephalin in organic solvents depend on solvent polarity. As compared with the reference model molecule of N-acetylphenylalanine methylamide, the rotamer populations of Phe4 of [Met5]-enkephalin are affected possibly by steric repulsion with other residues; the rotamer I is primarily favored but the rotamer II is appreciably destabilized in weakly polar solvents.

Amino Acid Sequence↗
PubMed1979

Nuclear-magnetic-resonance study on Met-enkephalin and Met-enkephalinamide. Molecular association and conformation.

The 270-MHz 1H and 68-MHz 13C nuclear magnetic resonance spectra of Met-enkephalin (Tyr-Gly-Gly-Phe-Met) and Met-enkephalinamide are analyzed in a variety of solvents. For the dipolar form of Met-enkephalin in (C2H3)2SO solution, significant concentration dependences are found of C-alpha proton chemical shifts, indicating an aromatic ring-current effect in molecular aggregates. An anomalous temperature dependence is observed of the amide proton chemical shift of the Met-5 residue. Furthermore, the chemical shifts of C-alpha protons of the dipolar form are found to depend appreciably on temperature. From the analyses of the temperature dependences together with concentration dependences of C-alpha proton resonances, the dipolar form of Met-enkephalin is found to be in an equilibrium of folded and extended conformations at low concentration in (C2H3)2SO solution. Solvent-composition dependences of the amide and C-alpha proton resonances and carbonyl and alpha-carbon resonances of the dipolar form in 2H2O/(C2H3)2SO solution are consistent with the conformation equilibrium and the association equilibrium. The folded conformation of the dipolar form in (C2H3)2SO solution is stabilized by the intramolecular attraction between the positively charged N-terminal group and negatively charged C-terminal group. The presence of the folded conformation is confirmed by the measurements of Gd(III)-induced relaxation enhancements of C-alpha protons. Nuclear Overhauser effects on the dipolar form are not consistent with the predominant formation of the beta-turn structure with the intramolecular hydrogen bond (Gly-2) C=O . H-N(Met-5). For the dipolar form of Met-enkephalin in 2H2O solution and for the cationic form of Met-enkephalinamide in (C2H3)2SO solution and in 2H2O solution there is no evidence for the formation of folded conformations.

Circular Dichroism↗