Search PubMed⌕ Search

Biomedical subjects

M Shimizu

Publications and source records attributed to M Shimizu.

At least 937 records · Page 52Linked to original sources
PubMed1992

The role of anticodon bases and the discriminator nucleotide in the recognition of some E. coli tRNAs by their aminoacyl-tRNA synthetases.

The T7 polymerase transcription system was used for in vitro synthesis of unmodified versions of the E. coli tRNA mutants that insert asparagine, cysteine, glycine, histidine, and serine. These tRNAs were used to qualitatively explore the role of some anticodon bases and the discriminator nucleotide in the recognition of tRNA by aminoacyl-tRNA synthetases. Coupled with data from earlier studies, these new results essentially complete a survey of all E. coli tRNAs with respect to the involvement of anticodon bases and the discriminator nucleotide in tRNA recognition. It is found that in the vast majority of tRNAs both of these elements are significant components of tRNA identity. This is not universally true, however. Anticodon sequences are unimportant in tRNA(Ser), tRNA(Leu), and tRNA(Ala) while the discriminator base is inconsequential in tRNA(Ser) and tRNA(Thr). The significance of these results for origin-of-life studies is discussed.

Amino Acyl-tRNA Synthetases↗
PubMed1992

Comparative teratogenicity of di-n-butyltin diacetate with n-butyltin trichloride in rats.

Teratological tests were conducted on di-n-butyltin diacetate (DBTA), and n-butyltin trichloride (MBTC). Pregnant Wistar rats were treated orally with DBTA at doses of 0, 1.7, 5.0, 10.0, and 15.0 mg/kg/day or with MBTC at doses of 0, 50, 100, 200, and 400 mg/kg/day during days 7-17 of gestation. Cesarean sections were performed on day 20 of gestation. Thymic atrophy of the pregnant rats was observed in a dose-dependent manner by DBTA treatment. The incidence of dead or resorbed fetuses and total resorption fetuses increased at the highest dose of DBTA. The incidence of fetuses with external malformations, such as cleft mandible, cleft lower lip, ankyloglossia (tongue-tie) and schistoglossia (cleft tongue), increased in a dose-dependent manner by DBTA treatment. The incidence of fetuses with skeletal malformations such as anomaly of mandibular fixation, fused ribs, fused cervical vertebral arches and fused thoracic vertebral arches also increased at 10.0 and 15.0 mg/kg. However, MBTC, one of the main metabolites of di-n-butyltin, failed to show any evidence of tetatogenic activity at any doses tested. The results indicate that DBTA has potent teratogenic effects on rat fetuses, and DBTA is different from MBTC with respect to teratogenic effects.

Animals↗
PubMed1992

The localization and characterization of proteinases for the initial cleavage of porcine amelogenin.

In the outermost layer of porcine-developing enamel adjacent to the ameloblasts in the secretory stage, the activities of two proteinases having molecular masses of 76 and 78kDa were detected by enzymography using gelatin as a substrate. On the other hand, high activities of known 30 and 34kDa proteinases were localized in the inner layer of the enamel. The 76kDa proteinase cleaved the carboxyl-terminal peptide of porcine 25kDa amelogenin to convert it to 20kDa amelogenin. The 78kDa proteinase also acted on the 25kDa amelogenin similarly, but its activity was weak. The results indicate that the 25kDa amelogenin synthesized and secreted by ameloblasts is converted to 20kDa amelogenin by the action of proteinase localized in the outermost layer of the secretory enamel, and then further degraded by the proteinases in the inner layer of the enamel associated with the increase of mineralization.

Amelogenin↗
PubMed1992

Usefulness of ultrasonography and Doppler color flow imaging in the diagnosis of internal jugular phlebectasia.

A 20-year-old woman presented to our hospital for investigation of a left neck mass. Ultrasonographic examination of the jugular mass demonstrated an echo-free space, the caliber of which markedly increased when the patient shifted from the sitting to the recumbent position or performed a Valsalva maneuver. On color Doppler flow imaging, a slow flow signal flowing in the direction opposite to that of the common carotid artery was found within this space. Ultrasonography and color Doppler flow imaging thus proved to be useful for correctly diagnosing internal jugular phlebectasia.

Adult↗
PubMed1992

D1 dopamine receptor binding in mood disorders measured by positron emission tomography.

D1 dopamine receptor binding in mood disorders was studied by positron emission tomography (PET) using 11C-SCH23390. Ten patients with bipolar mood disorders and 21 normal controls were studied in the drug-free state. The patients were in euthymic (N = 6), depressed (N = 3) and manic (N = 1) states. Regional radioactivity in the brain was followed for 40 min by PET. A two-compartment model was used to obtain the binding potential (k3/k4) for the striatum and frontal cortex. The binding potentials for the frontal cortex for the patients were significantly lower than those for normal controls, whereas those for striatum were not significantly different. These findings suggest that D1 dopamine receptors in the frontal cortex may be in a different state in patients with bipolar mood disorders.

Adult↗
PubMed1992

The effects of electroconvulsive shock or imipramine on subtypes of alpha 1-adrenoceptors in the frontal cortex of the rat.

The effects of repeated treatment (14 days) with electroconvulsive shock (ECS) or imipramine on binding sites on alpha 1-adrenoceptors in the rat were studied. The binding of [3H]prazosin studied with WB4101 and phentolamine, as binding inhibitors, showed the existence of two subtypes of alpha 1-adrenoceptor (alpha 1A and alpha 1B). Proportions of the alpha 1A and alpha 1B binding sites were about 3:7 in the frontal cortex and 9:1 in the hippocampus. Pretreatment of the membranes with chlorethylclonidine (CEC) almost abolished the alpha 1B binding sites. Inhibition of the binding of [3H]prazosin studied with antidepressants (imipramine, desipramine, maprotiline and mianserin) showed that these drugs bound to alpha 1-adrenoceptors with low affinity, in an apparent monophasic manner. The characteristics of the alpha 1A and alpha 1B binding sites were studied by the binding assay with [3H]prazosin, in the presence of a small concentration (2 nM) of WB4101 to mask the alpha 1A binding sites, as well as the assay without WB4101, for the total alpha 1-adrenoceptor (alpha 1A and alpha 1B) binding. Repeated treatment with electroconvulsive shock increased but that with imipramine decreased, the density of the alpha 1B binding sites in the frontal cortex, without change of the affinity. Neither treatment affected the alpha 1A binding sites in the frontal cortex. The alpha 1-adrenoceptors (alpha 1A and alpha 1B) in the hippocampus were not affected at all by these repeated treatments. The electroconvulsive shock-induced increase in the alpha 1B binding sites in the frontal cortex of the rat could contribute to differences in clinical effects between electroconvulsive shock and antidepressant drugs.

Adrenergic alpha-Antagonists↗
PubMed1992

Telescience testbed examination aboard Japanese Experiment Module (JEM): life and material science experiments.

A telescience ground testbed experiment was conducted by the National Space Development Agency of Japan (NASDA) at the Tsukuba Space Center in March 1991. The objectives of the ground testbed experiment were to extract scientists' requirements for a communication method, to evaluate the influence of transmission delay and capacity on experiment operations, and to evaluate performance and functions of the system for the testbed experiment. The microscopic operations experiment, the image furnace experiment and the onboard training experiment were selected as typical ground testbed experiments. In these experiments, motion video transmission at 320 kbps was acceptable for observing the experiments and communicating between the principal investigator and the payload specialist. In the microscopic operations experiment, motion video transmission at 1.5 Mbps or more was required for detailed observation. A 4-second transmission delay (roundtrip) was allowable for mutual communication.

Aerospace Medicine↗
PubMed1992

Role of gastric glutathione in smoke flavouring-induced gastric injury in rats.

Some commercial liquid smoke flavourings have been shown to induce acute gastric mucosal injury in rats when given orally as a large single dose. The present study was carried out to examine the mechanism of action in rats of two selected smoke flavourings containing about 10% total acids as acetic acid. These flavourings and 10% acetic acid decreased the concentration of glutathione (GSH) in the glandular stomach. The decrease in gastric GSH was coupled with smoke flavouring-induced gastric injury. Pretreatment with N-ethylmaleimide, a GSH depletor, enhanced acetic acid-induced gastric injury. Pretreatment with cysteine, a sulphhydryl compound, protected rats against smoke flavouring-induced gastric injury. Aqueous fractions of the smoke flavourings, after removal of non-polar compounds and acidic organic compounds (including acetic acid) by diethyl ether extraction, decreased the gastric GSH concentration considerably and had a marked reactivity in vitro with GSH, but these fractions by themselves showed no ability to induce gastric injury. Addition of 10% acetic acid to these aqueous fractions caused greater gastric injury than 10% acetic acid alone, which suggests that these aqueous fractions contain the (unidentified) compound(s) that facilitate acetic acid-induced gastric injury. These findings indicate that gastric endogenous and exogenous sulphhydryls play an important part in gastric cytoprotection.

Acetates↗
PubMed1992

Ordering of human chromosome 3p markers by radiation hybrid mapping.

To construct a panel of radiation hybrids (RHs) for human chromosome 3p mapping, mouse microcell hybrid cells, A9(neo3/t)-5, containing a single copy of human chromosome 3p with pSV2neo plasmid DNA integrated at 3p21-p22 were irradiated and fused to mouse A9 cells. A panel of 96 RHs that retain several sizes and portions of human chromosome 3p segments was used to map 25 DNA markers for chromosome 3p. Eight of them, H28, H29, H32, H33, H35, H38, H48, and H64, were cloned from Alu-primed PCR products using A9(neo3/t)-5 cell DNA as a template. The most likely order of the 24 markers, except for H28, based on the statistical ordering method proposed by Falk, was cen-D3S4-D3S3-D3S30-H29-D3S13-D3S2-+ ++H48-D3F15S2-D3S32-D3S23-CCK-H35-H33- D3S11-D3S12-RARB-THRB(ERBA2-pBH302)- H64-H38-RAF1-D3S18-H32-D3S22-pter. The order and location of these markers were in good agreement with those previously determined by other mapping methods, suggesting that a panel of these 96 RHs is a valuable source for a rapid mapping of human chromosome 3p markers.

Chromosome Mapping↗
PubMed1992

A case of transfusion-associated graft-versus-host disease not prevented by white cell-reduction filters.

A case of transfusion-associated graft-versus-host disease (TA-GVHD) in a patient with non-Hodgkin's lymphoma is reported. The patient, a 67-year-old woman, was diagnosed as having diffuse, mixed type non-Hodgkin's lymphoma, at clinical stage IIIA. She was treated with combination chemotherapy and received multiple blood transfusions for anemia and thrombocytopenia. Although white cells (WBCs) were reduced in the transfused components by WBC-reduction filters, the patient developed TA-GVHD that was confirmed by skin biopsy. It is suggested that the WBC reduction attained with these filters does not prevent TA-GVHD in immunocompromised patients. It is recommended that all blood components should be irradiated before transfusion to such patients.

Aged↗
PubMed1992

Activation of PC12 cells by lipophilic components of Panax ginseng.

The lipid soluble fraction of Panax ginseng C. A. Meyer has been found to possess a stimulatory effect on a para-neuronal culture cell line, namely PC12 cells. Addition of the diethyl ether extract (0.025-0.1 mg/ml) of Ginseng radix to a culture medium promoted the outgrowth of neurites from cells dose-dependently as well as their ready differentiation to respond to carbachol and high KCl-evoked membrane depolarization to induce free Ca2+ accumulation in the cells within a week of culture. Effective constituents of the extract were confined to four major substances detected in the extremely lipophilic front area on silica gel TLC.

Animals↗
PubMed1992

Exercise performance in essential hypertension with special reference to blood pressure response and left ventricular hypertrophy.

Exercise performance in essential hypertension (EH) and its relations to blood pressure (BP) response and left ventricular hypertrophy (LVH) were studied. Twenty-three patients with mild to moderate EH and 12 controls underwent symptom-limited (except BP elevation more than 250 mm Hg) ergometer exercise. Exercise performance was evaluated by the oxygen uptake (VO2/kg) at anaerobic threshold (AT) and at peak exercise (Peak). Left ventricular geometry and function, and left ventricular mass index (LVMI) were measured using echocardiography. The endpoints of 12 patients (group A) and controls were fatigue. The endpoints of 11 patients (group B) were BP elevation. Though both group A and group B had concentric hypertrophy, group B showed severe LVH compared to group A and controls. The VO2/kg at AT or at Peak was not different among the three groups. Neither BP response or LVMI correlated with exercise performance in EH. We conclude that exercise performance is not disturbed in EH; that BP response to exercise is not related to exercise performance in EH; and that concentric LVH may be a compensatory mechanism to maintain exercise capacity against exaggerated BP elevation in EH.

Adult↗
PubMed1992

Purification and properties of trimethylamine N-oxide reductase from aerobic photosynthetic bacterium Roseobacter denitrificans.

Trimethylamine N-oxide (TMAO) reductase was purified from an aerobic photosynthetic bacterium Roseobacter denitrificans. The enzyme was purified from cell-free extract by ammonium sulfate fractionation, DEAE ion exchange chromatography, hydrophobic chromatography, and gel filtration. The purified enzyme was composed of two identical subunits with molecular weight of 90,000, as identified by SDS-polyacrylamide gel electrophoresis, containing heme c and a molybdenum cofactor. The molecular weight of the native enzyme determined by gel filtration was 172,000. The midpoint redox potential of heme c was +200 mV at pH 7.5. Absorption maxima appeared at 418,524, and 554 nm in the reduced state and 410 nm in the oxidized state. The enzyme reduced TMAO, nicotine acid N-oxide, picoline N-oxide, hydroxylamine, and bromate, but not dimethyl sulfoxide, methionine sulfoxide, chlorate, nitrate, or thiosulfate. Cytochrome c2 served as a direct electron donor. It probably catalyzes the electron transfer from cytochrome b-c1 complex to TMAO reductase. Cytochrome c552, another soluble low-molecular-weight cytochrome of this bacterium, also donated electrons directly to TMAO reductase.

Bacteria↗
PubMed1992

Cyclophosphamide-induced suppressor cells in nude mice.

Lymphocytes regenerated after treatment with a high dose of cyclophosphamide (CY) were characterized in nude mice. Ten days after a single injection of 200 mg/kg CY into nude mice, regenerated spleen cells suppressed in vitro primary and second antibody production against sheep red blood cells. The CY-treated spleen cells exhibited normal natural killer (NK) activity, very low B and T cell content, but increases in cell surface charge [electrophoretic mobility (EPM)] and histamine receptors. The suppressor cells could not be removed by treatment with anti-Thy-1 plus complement (C), or treatment with antiasialo GM1 (aGM1) plus C, which abrogated NK activity. It was concluded that CY-treated spleen cells, which exhibited high EPM and histamine receptors, comprise the natural suppressor cells which are Ig-, Thy-1- and aGM-1.

Animals↗
PubMed1992

Stable nucleosome positioning and complete repression by the yeast alpha 2 repressor are disrupted by amino-terminal mutations in histone H4.

Nucleosomes are positioned in the presence of the yeast repressor alpha 2 in minichromosomes containing the alpha 2 operator and on the promoters of a-cell-specific genes regulated by alpha 2. To investigate the possibility that alpha 2 directs nucleosome position through an interaction with a component of the core particle, we analyzed chromatin structures adjacent to the operator in alpha cells containing mutations in the amino-terminal region of histone H4. Deletion or point mutation of specific amino acids in histone H4 altered the location and/or stability of nucleosomes adjacent to the alpha 2 operator. These changes in chromatin structure were accompanied by partial derepression of a beta-galactosidase reporter construct under alpha 2 control, even though alpha 2 remained bound to its operator sequence. Our data suggest that complete repression by alpha 2 requires stable positioning of nucleosomes in promoter regions and this positioning involves the conserved amino-terminal region of histone H4.

Base Sequence↗