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M Shimizu

Publications and source records attributed to M Shimizu.

At least 19 recordsLinked to original sources
PubMed1992

Escherichia coli tRNA(Asp) recognition mechanism differing from that of the yeast system.

Various tRNA transcripts were constructed to study the identity elements of Escherichia coli tRNA(Asp). Base substitutions from G34 to U34 at the first position of the anticodon, and from U35 to A35 at the second, severely impaired the aspartate charging activity. The activity was also decreased, but in a more moderate fashion, by base changes at G2-C71, C36 and C38. Identity nucleotides of tRNA(Asp) are distributed in a different fashion between E. coli and yeast, which occur at the second base pair of the acceptor stem, G10-U25 base pair in the D-stem and 3' half of the anticodon loop.

Anticodon↗
PubMed1992

Characterization of phospholipase D in a cell-free system of cultured cells derived from rat frontal cortex.

The existence and regulation of phospholipase D (PLD) activity in cell-free system from primary cultured cells of fetal rat frontal cortex were investigated. PLD activity was detectable only in the presence of Triton X-100. Other detergents examined (deoxycholate, taurocholate, CHAPS, Tween 20, sodium dodecyl sulfate) caused only a small increase in PLD activity. Triton X-100 enhanced PLD activity maximally at 0.1% (w/v) and reduced at higher concentrations. The optimal pH was about 7.2. Both Ca2+ and Mg2+ inhibited PLD activity in a dose-dependent manner. When comparing the primary cultured cells with adult rat frontal cortices, all of the results of the primary cultured cells were in agreement with those of the frontal cortices. Moreover, the apparent Km value of the enzyme in primary cultured cells for phosphatidyl-choline was the same as that in rat frontal cortex. These results suggest that the same kinds of PLD exist in the primary cultured cells and the rat frontal cortex, and that the primary cultured cells are a good experimental model for analyzing the mechanism of PLD in neuronal system.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1992

Effects of feeding and fasting on hepatolobular distribution of glutathione and cadmium-induced hepatotoxicity.

Relationship between hepatolobular distribution profile of glutathione (GSH) and cadmium (Cd)-induced hepatotoxicity was examined in both fed and fasted rats by computerized densitometry of histochemically stained GSH in the liver sections using an image analyzer system. In fed rats, density gradient distribution of hepatolobular GSH, which was higher in the periportal region than in the perivenous one, was always observed even at a diurnally minimal concentration of GSH. This heterogeneous distribution of GSH, however, disappeared in fasted rats, even though the hepatic GSH concentration recovered to 81% of the control level in rats fasted for 48 h. In histopathological examination on livers 24 h after oral treatment of fed and fasted rats with 60 mg Cd/kg, zonal necrotic changes were observed from the perivenous to midlobular region but not in the periportal one in fed rats even at a diurnally minimal concentration of hepatic GSH. On the other hand, necrotic changes in the liver extended to the panlobular region including the periportal one in fasted rats. These necrotic changes were greater with a longer duration of fasting. These results suggest that the density gradient distribution of hepatic GSH but not the actual concentration of the compound plays an important role in protecting rats against acute hepatotoxicity of Cd.

Animals↗
PubMed1992

Intracellular signal transduction for interleukin-1 beta-induced endothelin production in human umbilical vein endothelial cells.

The authors investigated the intracellular signal transduction for interleukin (IL)-1 beta-induced endothelin (ET) production by endothelial cells from cultured human umbilical vein (HUVEC). Cultured HUVEC released immunoreactive (iR)-ET into the media in a time-dependent manner and a significant increase of iR-ET production was observed by the addition of IL-1 beta. The stimulating effect of IL-1 beta on iR-ET production was respectively inhibited by protein kinase C (C kinase) inhibitor (H-7), Ca-calmodulin inhibitor (W-7), cyclic AMP-dependent protein kinase (A kinase) inhibitor (H-8) and tyrosine kinase inhibitor (genistain) in a dose-dependent fashion. The data suggested that intracellular signal transduction for IL-1 beta-induced iR-ET production were via such pathways as C kinase, A kinase, Ca-calmodulin and tyrosine kinase in combination or independently, though possible mediation by other pathways cannot be ruled out.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1992

Antidepressants inhibit spontaneous oscillations of intracellular Ca2+ concentration in rat cortical cultured neurons.

In rat cortical cultured neurons, spontaneous oscillations in the intracellular Ca2+ concentration ([Ca2+]i) were observed by direct [Ca2+]i measurements using the fluorescent indicator fura-2. These [Ca2+]i responses were eliminated by the removal of extracellular Ca2-, L-type Ca2+ channel blockers or a glutamate receptor antagonist. Three antidepressants (amitriptyline, imipramine and mianserin) suppressed the [Ca2+]i oscillations in the range of 1-50 microM. In addition, amitriptyline inhibited high K(+)-and glutamate-induced [Ca2+]i increases with IC50 values of 19 and 27 microM, respectively. Imipramine and mianserin also inhibited the high K(+)-induced [Ca2+]i increases with IC50 values of 45 and 24 microM, respectively. These results suggest that blocking actions by the antidepressants on voltage-dependent Ca2+ influx and glutamate receptor-mediated Ca2+ influx may be involved in the suppression of the [Ca2+]i oscillations.

Amitriptyline↗
PubMed1992

Fluorometric assay of 25-hydroxyvitamin D3 and 24R,25-dihydroxyvitamin D3 in plasma.

The first practical fluorometric assay of plasma 25-hydroxyvitamin D3 (25-OH-D3) and 24R,25-dihydroxyvitamin D3 (24,25-(OH)2D3) is described. The method uses a highly fluorescent dienophile, 4-[2-(6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydroquinoxalyl)ethyl]-1, 2,4- triazoline-3,5-dione (DMEQ-TAD), to fluorescence-label vitamin D. Vitamin D metabolites were roughly purified with a short cartridge column followed by HPLC, labeled with DMEQ-TAD, and the product was analyzed on HPLC. In the assay of 25-OH-D3 the new fluorometric method was compared with the HPLC-uv method and was confirmed to be as accurate and reliable (CV, 4-5%) as the HPLC-uv method. Plasma 24,25-(OH)2D3 was accurately assayed by the HPLC-FL method, where the standard addition method was successfully used to calculate the overall recovery.

24,25-Dihydroxyvitamin D 3↗
PubMed1992

Cardiac characteristics and postoperative courses in Cushing's syndrome.

To assess the cardiac characteristics and postoperative courses in patients with Cushing's syndrome, electrocardiography and echocardiography were performed to study 12 consecutive, unselected patients, and results were compared with those of essential hypertension and primary aldosteronism. Eleven patients had hypertension and 7 had diabetes mellitus. Before adrenalectomy, common electrocardiographic abnormalities consisted of high-voltage QRS complexes (10 patients) and negative T waves (7 patients). Echocardiograms showed left ventricular hypertrophy in 9 patients, and all the patients had evidence of asymmetric septal hypertrophy. In patients with left ventricular hypertrophy, the thickness of the interventricular septum ranged from 16 to 32 mm, whereas the ratio of the thickness of interventricular septum to that of the posterior wall ranged from 1.33 to 2.67. The interventricular septum in Cushing's syndrome was extremely thicker and asymmetric septal hypertrophy occurred more often than essential hypertension and primary aldosteronism. Nine patients could be followed up after operation. In these patients abnormal electrocardiographic findings had normalized, the thickness of interventricular septum had decreased and asymmetric septal hypertrophy had disappeared except in 1 patient. The reason why left ventricular hypertrophy in Cushing's syndrome is severe is still unknown. Because left ventricular hypertrophy is more severe and the frequency of asymmetric septal hypertrophy much greater in Cushing's syndrome than in essential and other secondary hypertension, it is thought that not only increased aortic pressure but excessive plasma cortisol may be etiologic factors in the progression of left ventricular hypertrophy in Cushing's syndrome.

Adrenal Gland Neoplasms↗
PubMed1992

Inhibitory effect of noradrenaline on acute liver injury induced by carbon tetrachloride in the rat.

The effect of exogenous noradrenaline (NA) on acute liver injury was investigated in rats receiving a single dose of carbon tetrachloride (CCl4). Animals were divided into the following groups: (I) no treatment, used for plasma catecholamine assay; (II) received CCl4 only; (III) treated with CCl4 plus noradrenaline (NA). Plasma levels of catecholamine (CA) were elevated in both groups II and III, particularly in NA: average value at 33 h after the exposure of CCl4 increased to 290-fold of the control in group II and to 513-fold in group III. Subsequently, the levels of NA decreased with time, and were comparatively well-preserved in the rats of group III. Hepatic changes observed in the animals of group II were as follows: destruction with reduced number in rough endoplasmic reticulum; destruction and disappearance of cristae in mitochondria, and numerous fat droplets (shown by electron microscopy); histologically observed marked centrilobular necrosis with steatosis followed by progression with time; and microangiographically demonstrated deranged intrahepatic microvasculature. By contrast, these changes were successfully prevented by NA treatment (group III). Furthermore, histologically observed centrilobular change was restored with time. It was concluded that, in a deranged state, NA takes a form quite dissimilar to ordinary state: Na exerts for hapatoprotective and is highly involved in liver injury.

Animals↗
PubMed1992

Oligo(2'-O-methyl)ribonucleotides. Effective probes for duplex DNA.

To find novel probes for duplex DNA, we prepared four types of triplexes containing a homopurine-homopyrimidine 15-mer duplex DNA, and examined their thermal stabilities (Tm values). The single strand used for triplex formation were a DNA 15-mer having a defined C-T mixed sequence, and its sugar-modified analogs, namely 2'-fluoro DNA, RNA, and 2'-O-methyl RNA. The 2'-O-methyl RNA and the RNA-containing triplexes were similar in their enhanced stabilities at pH 6.1 and, amongst the four triplexes, the 2'-O-methyl was the most stable at pH 5.0. Furthermore, an experiment using a 34-mer duplex DNA suggested that the 2'-O-methyl RNA-triplex was destabilized, mostly as a result of the incorporation of a mismatched triplet, as compared to the DNA triplex counterpart. Thus, 2'-O-methyl RNA can serve as an effective probe for duplex DNA.

Base Sequence↗
PubMed1992

In vitro study of E.coli tRNA(Arg) and tRNA(Lys) identity elements.

Various tRNA transcripts were constructed to study the identity elements of E.coli tRNA(Arg) and tRNA(Lys). Exchange of the anticodon of the major tRNA(Arg) from ACG to either CCG or CCU did not result in a significant loss of arginine acceptor activity, whereas not only that to UUU but also that to ACA or ACC decreased the activity. Base substitutions and deletion at A20 also impaired the arginine charging activity by over 50-fold. Arginine charging activity was introduced by either substitution of the anticodon from UAC to ACG in tRNA(Val) or from UUU to UCU in tRNA(Lys). Only a single base substitution at the third position of tRNA(Trp) anticodon (CCA) from A to G also gave rise to arginine charging activity, which was elevated to a comparable level to that of the tRNA(Arg) transcript by an additional A20 insertion. Base substitutions of the major tRNA(Arg) at the discriminator position into pyrimidines led to a decrease by factors of three to four. These data show that the third letter of the anticodon G36 or U36 besides the second letter C35 and the A20 in the variable pocket is responsible for the arginine acceptor identity, to which the discriminator base A73 or G73 contributes in an auxiliary fashion. In contrast to the arginine system, the transcript with the wild-type tRNA(Lys) sequence showed only 140-fold lower lysine charging activity than the native tRNA(Lys), suggesting the involvement of base modifications in recognition. Replacement of the anticodon UUU with not only UCU and UAC but also UUA and UUC seriously affected the lysine acceptor activity, and those with GUU and UUG also decreased by factors of 17 and 5, respectively. Introduction of UUU into the anticodons conferred lysine charging activity upon both tRNA(Val) and tRNA(Arg). Substitution of the discriminator base A73 by any of the other bases decreased the lysine acceptor activity by a factor of ten. These results indicate the involvements of all the three bases of the anticodon and A at the discriminator position in lysine specific aminoacylation.

Anticodon↗
PubMed1992

[Quantitative evaluation of liver function using 99mTc-GSA in rats with liver injury induced by ischemia-reperfusion].

We evaluated quantitatively the liver injury of rats induced by ischemia-reperfusion, using 99mTc-DTPA-Galactosyl-Human-Serum-Albumin (99mTc-GSA). The vessels of the left lobe were clamped for 5, 10, or 45 minutes followed by 15 minutes reperfusion. Then, 99mTc-GSA was intravenously administered (170 micrograms/kg body weight) to rats. Two compartment analysis was made on measurement curves in the heart and liver to obtain clearance parameters. Significant difference was observed between the ischemic group (clamped for 10 and for 45 minutes) and the control. These results suggest that 99mTc-GSA is useful in the estimation of liver injury produced by ischemia-reperfusion.

Animals↗
PubMed1992

Identity determinants of E. coli threonine tRNA.

To investigate the identity determinants of E. coli threonine tRNA, various transcripts were prepared by in vitro transcription system with T7 RNA polymerase. Substitutions of the anticodon second letter G35 and the third letter U36 to other nucleotides led to a remarkable decrease of threonine charging activity. Charging experiments with a series of anticodon-deletion transcripts also suggest the importance of the G35U36 sequence. A mutation at either the G1-C72 or C2-G71 base pair in the acceptor stem seriously affected the threonine charging activity. These results indicate that the second and third positions of the anticodon and the first and second base pairs in the acceptor stem are the recognition sites of E. coli tRNA(THR) for threonyl-tRNA synthetase. Discriminator base, A73, is not involved in threonine charging activity.

Base Sequence↗
PubMed1992

Preferential binding of E.coli histone-like protein HU alpha to negatively supercoiled DNA.

Binding specificity of histone-like HU alpha protein to supercoiled DNA was examined by gel retardation assay and chemical probing with OsO4. The latter method was proved to be a unique means for detecting torsional tension restrained in supercoiled plasmid in the presence of HU alpha. It was shown that HU alpha protein has preferential affinity to negatively supercoiled DNA relative to relaxed, nicked and linearized DNAs. There were two modes for binding of HU alpha to the supercoiled DNA: one was the binding associated with topological changes in DNA and the other was relatively strong binding, probably specific to certain particular structures of DNA. It was suggested that HU in vivo interacts preferentially with the regions deformed under torsional stress or with the metabolically active regions along DNA.

Bacterial Proteins↗
PubMed1992

Synthesis of receptor antagonists of neuropeptide Y.

We report the synthesis of receptor antagonists of neuropeptide Y (NPY) by a strategy based on synthesis of mixtures of analogs and the subsequent isolation and identification of receptor antagonists from these mixtures. After screening a series of mixtures of NPY analogs by using an NPY antagonist assay, two potent receptor antagonists, designated PYX-1 and PYX-2, were isolated from an antagonist-containing mixture. Structural analysis revealed these analogs to be Ac-[3-(2,6-dichlorobenzyl)Tyr27, D-Thr32]NPY-(27-36) amide and Ac-[3-(2,6-dichlorobenzyl)Tyr27,36,D-Thr32]NPY-(27-36) amide, respectively. The receptor antagonists inhibited release of intracellular calcium elicited by NPY in human erythroleukemia cells and displaced 3H-labeled NPY from NPY receptors in rat brain membrane. The approach of screening and identifying useful analogs from synthetic mixtures may significantly reduce the time and resources previously required for development of receptor antagonists.

Amino Acid Sequence↗
PubMed1992

Structure of the human pituitary adenylate cyclase activating polypeptide (PACAP) gene.

The human gene encoding pituitary adenylate cyclase activating polypeptide (PACAP) was isolated and its nucleotide sequence was determined. By comparison with a human PACAP cDNA, the exon/intron organization of PACAP gene was determined. The last exon encoded the longer form of PACAP, PACAP38 and 3'-untranslated sequences, suggesting that the shorter form of PACAP, PACAP27 is not generated by alternative splicing mechanisms. The 5'-flanking region of the PACAP gene contains several sequence motifs homologous to CRE, TRE, and GHF-1. On the basis of DNA isolated from mouse A9 microcell hybrid clone containing a single human chromosome, the PACAP gene was assigned to human chromosome 18. Furthermore, we determined the locus of the gene to be 18p11 by the chromosomal in situ hybridization technique.

Amino Acid Sequence↗
PubMed1992

Cell electrophoretic characterization of abnormally expanded lymphocytes in autoimmune lprcg, lpr, gld and Yaa mice, and of thymocyte subsets.

Autoimmune mice carrying the lprcg/lprcg(lprcg),lpr/lpr(lpr),gld/gld(gld) and Yaa genes exhibit massive lymphoproliferation and a systemic lupus erythematosus-like syndrome. The surface markers of abnormally expanded lymphocytes used were Thy-1+, CD4-CD8- (double negative, DN) and CD45+ for lprcg, lpr, gld and (lprcg X gld) hybrid (F1-lprcg-gld) mice, and Ig+ for Yaa mice. To characterize the cell surface properties and differentiation pathway of lymphocytes in autoimmune mice, the cell electrophoretic mobility (EPM) was determined for the lymph node (LN), spleen and thymus cells. The EPM of lymphocytes derived from swollen LN was of the T cell type in lprcg, lpr, gld and F1-lprcg-gld mice, but of the B cell type in Yaa mice, indicating that the EPM of abnormally proliferated lymphocytes in autoimmune mice reflects their origin, and that the surface properties detected as a net negative charge were the same in abnormal and normal lymphocytes. The electrophoretic behavior of whole thymocytes was also the same in autoimmune and normal mice. The DN, and CD4+CD8- and CD4-CD8+ (single positive, SP) thymocytes from normal mice exhibited high EPM, while CD4+CD8+ (double positive, DP) thymocytes exhibited low EPM. According to the recent concept of intrathymic T cell differentiation (Schwartz, R. H., Cell. 1989, 57, 1073-1081), it is suggested that EPM of thymocytes may change with maturation in the following manner: DN thymocytes with high EPM----DP thymocytes with low EPM----SP thymocytes and autoimmune DN T cells with high EPM.

Animals↗
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↗