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Biomedical subjects

T Shibata

Publications and source records attributed to T Shibata.

At least 1,009 records · Page 56Linked to original sources
PubMed1984

[Subacute toxicity of an amine-curing agent for epoxy resin].

Amine-curing agent for epoxy resin, bis(4-amino-3-methylcyclohexyl)methane, has been suspected of inducing toxic symptoms in man which resemble collagen disease such as scleroderma or polymyositis. We studied subacute toxicity of this agent by repeated oral administrations to rats. The agent was administered 25, 37.5, 50, 75 or 100 mg/kg per one dose, 8 times in 10 days or 17 times in 4 weeks or 20-22 times in 4 weeks. When administration had been completed, clinical biochemical tests and histopathological examinations were carried out. Animals of high dosage group showed suppression of body weight increase and loss of muscular strength of limbs in the administration period. By clinical biochemical tests, elevation of blood components from muscle (CPK, GOT, creatine) was noticed. Also, increase of monoamine oxidase and decrease of alkaline phosphatase were revealed. By histological examinations, skeletal muscle and choroid plexus of brain showed noticeable changes. In muscles of high dosage group, atrophy, degeneration and regeneration of muscle fibers were observed and an increase of fibroblasts was also seen. In choroid plexus, vacuolar changes in epithelial cells were observed, being clearly dose-dependent. No particular change was recognized in skin. Though scleroderma-like change was not observed in the skin histologically, our results suggest that this amine-curing agent was greatly associated with muscle symptoms in the workers who handled epoxy resin and that it was one of causative agents which induced toxic symptoms like those of collagen disease.

Animals↗
PubMed1983

ATP-dependent unwinding of the double helix and extensive supercoiling by Escherichia coli recA protein in the presence of topoisomerase.

recA protein, which is essential for genetic recombination in Escherichia coli, causes extensive unwinding of the double helix by an ATP-dependent reaction and accumulation of positive supercoiling in closed circular double-stranded DNA. Initiation of the extensive unwinding was largely dependent on homologous single-stranded DNA. Therefore, it is likely that the extensive unwinding is initiated mainly at the site of D-loops. "Nascent D-loops" in which the two DNA molecules did not interwind were also good initiation sites of extensive unwinding. When the concentration of Mg2+ was decreased from the standard conditions for D-loop formation (13 mM MgCl2; the higher Mg2+ condition) to the lower Mg2+ condition (1 to 2 mM MgCl2), extensive unwinding by recA protein was initiated very quickly in the absence of single-stranded DNA. Results showed that this single-stranded DNA-independent initiation of extensive unwinding (i) requires negative superhelicity of the double-stranded DNA and (ii) is a first order reaction with respect to the DNA. These observations suggest that, under the lower Mg2+ condition, the extensive unwinding starts at a transiently denatured site in the negative superhelical DNA. Once initiated, the unwinding by recA protein is propagated extensively, even under conditions that do not allow its initiation. Therefore, the propagation of unwinding is a processive reaction ("processive unwinding"). Previous studies indicated that recA protein promotes "distributive unwinding" of double helix which depends on single-stranded DNA. Therefore, recA protein promotes unwinding of the double helix by either of two distinct pathways. Stress caused by the processive unwinding could explain the dissociation of D-loops and reversible inactivation of the double-stranded DNA in a D-loop cycle.

Adenosine Triphosphate↗
PubMed1983

A new class of site-specific endodeoxyribonucleases. Endo.Sce I isolated from a eukaryote, Saccharomyces cerevisiae.

We had found that yeasts had intracellular endodeoxyribonucleases that cut phage DNA into a set of double-stranded fragments with discrete chain lengths. We purified one of them to apparent homogeneity from Saccharomyces cerevisiae and designated it Endo.Sce I. Sequence analysis around 5 cleavage sites in plasmid DNA and phage DNA revealed that Endo.Sce I cuts a defined phosphodiester bond in each strand of double helix at the cleavage sites and produces free cohesive ends consisting of 4 nucleotides protruding at 3'-termini. However, unlike in the case of prokaryotic type II-restriction endonucleases, (i) Endo.Sce I seems to consist of two nonidentical subunits, (ii) no common palindrome or consensus sequence including more than 5 base pairs is detected at or near these cleavage sites, and (iii) Endo.Sce I can cut the DNA isolated from the cells that produced Endo.Sce I. All of the 5 cleavage sites are included in inverted repeats, but these inverted repeats are variable in size, nucleotide sequence, and distance between repeating units. An inverted repeat itself is not a structure recognized by Endo.Sce I. This study shows that Endo.Sce I is the first example of eukaryotic site-specific endonuclease and has properties, as described above, which distinguish it from prokaryotic restriction endonucleases.

Base Sequence↗
PubMed1983

Selective 31P(1H) nuclear Overhauser effect study on the polar headgroup conformation of phospholipids in micelles in organic solvents.

The polar headgroup structure of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) in inverted micelles in chloroform or benzene was investigated by the selective 31P(H) nuclear Overhauser effect (NOE). In the frequency dependence of the 31P(1H) NOE, PC micelles in CDCl3 showed two maxima. The larger maximum was located at the resonance of the glycerol-CH2OP protons and the smaller at the resonance of the N-methyl protons. In PC/PE mixed micelles in C6D6, both PC and PE showed three maxima which were located at the resonance of the CH2OP protons, the N-methyl protons and the amino protons in the frequency dependence of the 31P-NOE. The N-methyl protons of PC and the amino protons of PE were closely spaced to the phosphate groups of neighboring lipid molecules. The polar headgroups of PC and PE in the mixed micelles were concluded to lie in the plane perpendicular to the molecular axes. The frequency dependence of the 31P(H) NOE for PS micelles in C6D6 showed the maxima at the resonances of the amino protons and the CH2OP protons. The polar headgroups of PS molecules were not extended parallel to the molecular axes in the inverted micelles.

Magnetic Resonance Spectroscopy↗
PubMed1983

Synthesis and in vitro activity of a new carbapenem, RS-533.

The synthesis and in vitro antimicrobial activity of a new synthetic carbapenem, (5R,6S)-6-[(R)-1-hydroxyethyl]-2-[(S)-1-acetimidoylpyrrolidin -3-ylthio]-1-carbapen-2-em-3-carboxylic acid (RS-533), are described. The MIC values of related penems and carbapenems are also given for comparison with those of the new carbapenem.

Anti-Bacterial Agents↗