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Biomedical subjects

S Nishimura

Publications and source records attributed to S Nishimura.

At least 847 records · Page 47Linked to original sources
PubMed1982

Isolation and characterization of an Escherichia coli mutant lacking tRNA-guanine transglycosylase. Function and biosynthesis of queuosine in tRNA.

An E. coli mutant that lacks tRNA-guanine transglycosylase was isolated by random screening from a collection of Escherichia coli mutants obtained with N-methyl-N'-nitro-N-nitrosoguanidine. The defective gene, named tgt, was mapped at about 9 min on the E. coli chromosome, and the gene order was shown to be phoB-tgt-tsx. tgt was transferred to an E. coli strain with a defined genetic background by P1 transduction to investigate its function. The mutant thus obtained lacked queuosine (2-amino-5-[3S, 4R, 5S)-4,5-dihydroxycyclopent-1-en-3-ylaminomethyl]-7-(beta-D-ribofuranosyl)-pyrro lo-[2,3-D]-pyrimidin-4-one) in tRNA, indicating that the enzyme is actually involved in the biosynthesis of queuosine in tRNA. No clear biological defect was observed in the mutant, and, in fact, it grew slightly faster than the control isogenic strain. tRNATyr lacking queuosine, isolated from the mutant, showed no significant biological difference from normal queuosine-containing tRNA in amino acid acceptor activity or amino acid transfer in a cell-free protein synthesizing system directed by synthetic polynucleotide. The only phenotypic change observed in the mutant thus far is marked reduction of viability when the cells are kept under unsuitable conditions for growth, suggesting that the presence of queuosine in tRNA is important to E. coli for survival in the natural environment.

Escherichia coli↗
PubMed1982

Structure of a modified nucleoside in archaebacterial tRNA which replaces ribosylthymine. 1-Methylpseudouridine.

The structure of a modified nucleoside isolated from Halococcus morrhuae tRNA has been established as 1-methylpseudouridine, based on mass spectrometry and gas chromatography carried out on 0.2 A260 unit of material. Not previously found in nucleic acids, 1-methylpseudouridine appears to be unique to archaebacterial tRNA, where it replaces ribosylthymine in the T psi C loop of most of the tRNAs examined thus far.

Chromatography, Gas↗
PubMed1982

Studies on the metabolism of unsaturated fatty acids. VIII. Induction of 2,4-dienoyl-CoA reductase in Escherichia coli on the addition of unsaturated fatty acids.

2,4-Dienoyl-CoA reductase has been detected in crude extracts of E. coli. The reductase was shown to be induced many fold when the cells were grown in the presence of linoleic or oleic acid. The activity profile of the reductase on gel filtration was different from those of other enoyl reductases. These results suggest that there are two pathways even in E. coli for the degradation of cis-4-decenoyl-CoA, which is an intermediate in the beta-oxidation of linoleic acid, as recently proposed in rat liver.

Chemical Phenomena↗
PubMed1982

Studies on the metabolism of unsaturated fatty acids. X. Purification and some properties of 2,4-dienoyl-CoA reductase from Escherichia coli.

2,4-Dienoyl-CoA reductase has been separated from Escherichia coli grown in the presence of linoleic acid and purified to homogeneity. The enzyme has a molecular weight close to 50,000 as determined by gel filtration on Sephacryl S-200 Super-fine. The reductase was rather stable in a buffer containing citric acid and kept its full activity on heating at 55 degrees C for 10 min in the pH range of 5.5 to 6.5, but was completely inactivated on heating at 58 degrees C for 10 min. Phosphocellulose column chromatography revealed that the reductase was not involved in the multi-enzyme complex (molecular weight of 260,000) of fatty acid oxidation.

Escherichia coli↗
PubMed1982

Identification of nucleosides in hydrolysates of transfer RNA by high-resolution mass spectrometry.

High-resolution mass spectrometry has been investigated as a technique for identification of modified nucleosides in unfractionated hydrolysates of transfer RNA. The method is based on recognition of predetermined sets of exact mass values which are characteristic of individual nucleoside components. Mass spectra are photographically recorded in a non-time-resolved fashion, so that differing rates of nucleoside vaporization are of no consequence. Experimental parameters of sensitivity, spectrometer resolution and rates of vaporization were studied. Under typical conditions, 1-4 micrograms of tRNA are hydrolyzed, converted to volatile trimethylsilyl derivatives, and mass spectra of the resulting mixture recorded during 3 min at resolution 20 000; 75-100% of the minor nucleosides are usually identified in a single recording. The method is complementary to conventional methods of identification which rely on chromatographic mobilities, and can in principle be generally applied to recognition of biologically or chemically modified bases in nucleic acid.

Chemical Phenomena↗
PubMed1982

Homologous Terminal Sequences in the Double-Stranded RNA Genome Segments of Cytoplasmic Polyhedrosis Virus of the Silkworm Bombyx mori.

The 3'-terminal regions (20 to 32 residues) of the genome double-stranded RNA (dsRNA) segments of cytoplasmic polyhedrosis virus were sequenced. The dsRNAs, which were labeled at their 3' termini by incubation with [5'-(32)P]pCp and T4 RNA ligase, were denatured and resolved into the plus and minus strands by agarose-urea gel electrophoresis. Ten single-stranded RNAs thus obtained from the five dsRNA segments IV, V, VIII, IX, and X were sequenced by postlabeling methods. Common 3'-terminal sequences, -GUUAGCC and -UUACU, were found in the plus and minus strands, respectively, of all five dsRNA segments. However, adjacent sequences diverged and were considerably variable. The homologous sequences found in the 3' end may be important recognition signals for viral RNA polymerases and for assembly of the genome segments.

Journal Article↗
PubMed1982

Mechanism of choline-induced secretion of catecholamines from the cat adrenal medulla: involvement of nicotinic receptor.

Cat adrenal glands were retrogradely perfused in vitro with modified Locke's medium and the mechanism of catecholamine (CA) secretion induced by choline was investigated. Choline-induced secretion of CA was accompanied by release of dopamine-beta-hydroxylase, but not by that of phenylethanolamine-N-methyl transferase, indicating that an exocytotic mechanism is involved in the secretion. Choline failed to induce the secretion of CA when Ca was absent from the perfusion solution. On the other hand, secretion increased when the concentration of Ca2+ in the perfusion medium was raised to 10 mM. Stimulation of secretion by choline was observed from a concentration of 1 mM, and half-maximal secretion occurred at about 10 mM. The stimulatory action was weaker than that of acetylcholine(ACh); the effect of 100 mM choline was approximately equal to that of 0.02 mM ACh. Secretion induced by a low concentration of choline was abolished by a nicotinic blocker, hexamethonium, while the response to choline at a concentration higher than 130 mM was only partially inhibited by cholinergic antagonists. The effects of choline and a low concentration of ACh were additive. On the other hand, 100 mM choline inhibited the response to a supramaximal concentration of ACh(0.5 mM), suggesting that ACh and choline stimulate the same nicotinic receptor. It is concluded that choline acts partially as a nicotinic agonist and that a concentration higher than 130 mM causes secretion by a mechanism additional to nicotinic receptor activation.

Acetylcholine↗
PubMed1982

The binding of kappa- and sigma-opiates in rat brain.

Detailed displacements of [3H]dihydromorphine by ketocyclazocine and SKF 10,047, [3H]ethylketocyclazocine by SKF 10,047, and [3H]SKF 10,047 by ketocyclazocine are all multiphasic, suggesting multiple binding sites. After treating brain tissue in vitro with naloxazone, all displacements lose the initial inhibition of 3H-ligand binding by low concentrations of unlabeled drugs. Together with Scatchard analysis of saturation experiments, these studies suggest a common site which binds mu-, kappa, and sigma-opiates and enkephalins equally well and with highest affinity (KD less than 1 nM). The ability of unlabeled drugs to displace the low affinity binding of [3H]dihydromorphine (KD = 3 nM), [3H]ethylketocyclazocine (KD = 4 nM), [3H]SKF 10,047 (KD = 6 nM), and D-Ala2-D-Leu5-[3H]enkephalin (KD = 5 nM) remaining after treating tissue with naloxazone demonstrates unique pharmacological profiles for each. These results suggest the existence of distinct binding sites for kappa- and sigma-opiates which differ from those sites which selectively bind morphine (mu) and enkephalin (delta).

Animals↗