PubMed Health⌕ Search

Biomedical subjects

T Komatsubara

Publications and source records attributed to T Komatsubara.

At least 19 recordsLinked to original sources
PubMed2002

Magnetic structure, phase diagram, and a new type of spin-flop transition dominated by higher order interaction in a localized 5f system U3Pd20Si6.

The magnetic structure of the localized-5f uranium intermetallic compound U3Pd20Si6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling.

Journal Article↗
PubMed2001

Evolution of quasiparticle properties in UGe(2) with hydrostatic pressure studied via the de Haas-van Alphen effect.

We report measurements of the de Haas-van Alphen effect in UGe (2) under hydrostatic pressures up to 17.6 kbar, exceeding the critical pressure P(c) for the suppression of ferromagnetism. A discontinuous change of the Fermi surface is found to occur across P(c). Substantially enhanced effective masses (approximately 40m(e)) are found near P(c) on both the ferromagnetic and the paramagnetic sides.

Journal Article↗
PubMed2001

Strong coupling between local moments and superconducting 'heavy' electrons in UPd2Al3.

The electronic structure of heavy-fermion compounds arises from the interaction of nearly localized 4f- or 5f-shell electrons (with atomic magnetic moments) with the free-electron-like itinerant conduction-band electrons. In actinide or rare-earth heavy-fermion materials, this interaction yields itinerant electrons having an effective mass about 100 times (or more) the bare electron mass. Moreover, the itinerant electrons in UPd2Al3 are found to be superconducting well below the magnetic ordering temperature of this compound, whereas magnetism generally suppresses superconductivity in conventional metals. Here we report the detection of a dispersive excitation of the ordered f-electron moments, which shows a strong interaction with the heavy superconducting electrons. This 'magnetic exciton' is a localized excitation which moves through the lattice as a result of exchange forces between the magnetic moments. By combining this observation with previous tunnelling measurements on this material, we argue that these magnetic excitons may produce effective interactions between the itinerant electrons, and so be responsible for superconductivity in a manner analogous to the role played by phonons in conventional superconductors.

Journal Article↗
PubMed1999

Residual short-range order in the heavy fermion compound CeInCu2.

By using the X-ray diffraction technique, residual short-range order was detected in CeInCu(2), cerium dicopper indium, which is known to be a heavy fermion compound. In spite of the long-range order of this substance, diffuse scattering exhibiting short-range order was observed at room temperature. The correlation parameters obtained showed that an incorrectly occupied lattice site has a tendency to gather atoms of different species at the neighboring sites along the <111> directions. Thus, the disordered region would form a cluster composed of several disordered atoms. Furthermore, a chain-type correlation which has a period of 20-23 Å along the same directions was indicated. The superstructure-like feature of the disordered atoms hardly increases the residual resistivity. It is consistent with the behavior of the residual resistivity under high pressure.

Journal Article↗
PubMed1998

Identification of functional domains of rat intestinal phospholipase B/lipase. Its cDNA cloning, expression, and tissue distribution.

A cDNA encoding a rat intestinal Ca(2+)-independent phospholipase B/lipase (PLB/LIP) was cloned from an ileac mucosa cDNA library using a probe amplified by polymerase chain reaction based on the purified enzyme's sequence. PLB/LIP consists of an NH2-terminal signal peptide, four tandem repeats of about 350 amino acids each, and a hydrophobic domain near the COOH terminus. The enzyme purified previously was found to be derived from the second repeat part. To examine the function of each domain, the full-length PLB/LIP, individual repeats, and a protein lacking the COOH-terminal hydrophobic stretch were expressed in COS-7 cells. The results showed that the second repeat, but not the other repeats, had all the activities (phospholipase A2, lysophospholipase, and lipase) found in the purified natural and expressed full-length enzymes, suggesting repeat 2 is a catalytic domain. The full-length enzyme was mainly present in membrane fractions and efficiently solubilized by treatment with 1% Triton X-100, but not with phosphatidylinositol-specific phospholipase C. Deletion of the COOH-terminal hydrophobic stretch caused the secretion of > 90% of synthesized PLB/LIP into culture media. These results suggest the hydrophobic domain is not replaced by a glycosylphosphatidylinositol anchor but serves as a membrane anchor directly. A message of the full-length PLB/LIP was abundantly expressed in the ileum and also, in a smaller, but significant amount, in the esophagus and testis. Immunohistochemistry showed that PLB/LIP is localized in brush border membranes of the absorptive cells, Paneth cells, and acrosomes of spermatid, suggesting its roles related and unrelated to intestinal digestion.

Amino Acid Sequence↗
PubMed1995

Augmented sensitivity to benzodiazepine in septic shock rats.

The purpose of this study was to assess the pharmacological characteristics of the benzodiazepine binding site in the brain of septic animals. We induced endotoxin shock in rats using a caecum ligation and puncture model. Following examination of the physiological state of the rats 24 hr after the caecum ligation and puncture, brain tissue samples were prepared for biochemical assay of amino acids and for the [3H]-diazepam radioligand binding assay. Amino acids assays indicated that the concentration of aromatic amino acids was higher in the CLP group (P< 0.05), the branched chain amino acid concentration was lower in the CLP group (P< 0.05) and the sulfur-containing amino acid concentration was elevated in the CLP group (P< 0.05) than in both the control and the sham-operated groups. [3H]-diazepam radioligand binding assays demonstrated that the number of receptors in the septic rats was increased in the forebrain (CLP rats; 2.37 +/- 0.04 pmol x mg(-1) protein, control rats; 1.45 +/- 0.02 pmol x mg(-1) protein, sham-operated rats; 1.49 +/- 0.03 pmol x mg(-1) protein), cerebellum (CLP rats; 1.55 +/- 0.05 pmol x mg(-1) protein, control rats; 1.05 +/- 0.02 pmol x mg(-1) protein, sham-operated rats: 1.09 +/- 0.02 pmol x mg(-1) protein) and brain stem (CLP rats; 1.21 +/- 0.04 pmol x mg(-1) protein, control rats; 0.61 +/- 0.02 pmol x mg(-1) protein, sham-operated rats; 0.63 +/- 0.02 pmol x mg(-1) protein) compared with the control and sham-operated rats (P< 0.05). In conclusion, it was considered that the increased number of benzodiazepine receptors may be one cause of the neuronal alteration observed in septic shock animals.

Amino Acids↗
PubMed1994

Enhanced expression of group II phospholipase A2 in human hepatocellular carcinoma.

Enzyme activity, protein contents, and mRNA contents of group II phospholipase A2 (PLA2) in hepatocellular carcinoma (HCC) surgically obtained from 8 patients were compared with those in either its neighboring liver tissues or control liver tissues. The PLA2 specific activity towards the mixed micelles of 1-palmitoyl-2-oleoyl-phosphatidylglycerol and cholate was significantly greater in the tumor tissues (6.62 +/- 1.46 nmol/min/mg) than those in the surrounding liver tissues (1.33 +/- 0.22 nmol/min/mg) and controls (0.43 +/- 0.04 nmol/min/mg). The results of immunoblot analysis using a specific anti-human group II PLA2 antibody and of Northern blot analysis using a human group II PLA2 cDNA as a probe demonstrated that group II PLA2 was responsible for the increased enzyme activity. The contents of immunoreactive group II PLA2 in the tumor tissues (8.81 +/- 1.24 ng/mg) were significantly higher than those in the surrounding liver tissues (1.74 +/- 0.27 ng/mg); those in the control tissues were below the analytical range of the method used. The group II PLA2 mRNA was also significantly increased in the tumor tissues, compared with that in the surrounding liver tissues, whereas it was not detectable in the controls. This indicates that group II PLA2 in HCC is induced at the pretranslational level.

Carcinoma, Hepatocellular↗