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Biomedical subjects

S Nishimura

Publications and source records attributed to S Nishimura.

At least 739 records · Page 41Linked to original sources
PubMed1986

Detection and identification of mutagens by the adducts formed upon reaction with guanosine derivatives.

Mutagens present in crude samples such as heated glucose can be detected or identified by means of the adducts formed upon reaction with a fluorescent guanosine derivative (FG) or isopropylideneguanosine (IPG). After the reaction of IPG with heated glucose, two adducts were isolated by high-performance liquid chromatography. One of the adducts was identified as the cyclic adduct formed between IPG and glyoxal. Mesoxaldialdehyde, which is structurally related to glyoxal, also produced a cyclic IPG-adduct and showed mutagenic activity in Salmonella typhimurium strain TA100. The other adduct isolated from the reaction mixture of IPG and heated glucose was 8-hydroxy-IPG. Various reagents which generate oxygen radicals were effective in the hydroxylation of guanosine derivatives at the C-8 position. These reagents also cause hydroxylation of guanine residues in DNA.

Chromatography, High Pressure Liquid↗
PubMed1986

Prazosin selectively antagonizes norepinephrine contractions at low-affinity, non-alpha adrenoceptor sites (extraceptors) in arterial muscle.

The characteristics of a low-affinity site activated by norepinephrine (NE), which is demonstrable in arterial smooth muscle pretreated with phenoxybenzamine (PBZ) to alkylate most alpha adrenoceptors were studied. Treatment with PBZ resulted in biphasic dose-response curves to NE. The initial phase associated with concentrations of NE up to 10(-5) M was due to its action in tissues where alpha adrenoceptors have been reduced to a number that would not support a maximum contraction. The second phase occurred with higher doses of NE. We postulate that this latter PBZ-resistant phase or contraction, which can represent more than 60% of the control maximal response, occurs at low-affinity sites for NE "extraceptors" distinct from alpha adrenoceptors in arterial smooth muscle. These residual responses to NE after PBZ treatment were inhibited selectively by prazosin and protected by prazosin from further inhibition by additional doses of PBZ. Effects due to prazosin at low-affinity sites were observed only with doses in excess of those required to competitively inhibit responses through alpha adrenoceptors in smooth muscle. The response to NE occurring through PBZ-resistant adrenoceptors was not dependent on the presence of the endothelium. This low-affinity site for NE was also evident after alkylation of alpha adrenoceptors with other irreversibly acting antagonists (e.g., benextramine and dibenamine). These observations are discussed in relation to the suggestion for a new adrenoceptor, the gamma-adrenoceptor. Differences and similarities of the extraceptor with this proposed adrenoceptor are discussed. Both sites have a high threshold to NE, and both may be influenced by prazosin.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1985

Two tRNAIle1 species from an extreme thermophile, Thermus thermophilus HB8: effect of 2-thiolation of ribothymidine on the thermostability of tRNA.

From Thermus thermophilus HB8 grown at 65 degrees C, two major tRNAIle species have been purified by column chromatography and polyacrylamide gel electrophoresis. The nucleotide sequence of one of these two tRNAIle1 species (tRNAIle1a) has been determined to be pGGGCGAUUAGCUCAGCUGmGUDAGAGCGCACGCCUGAUt6AAGCGUGAGm7GUCGGUGGs2T psi CAm1AGUCCACCAUCGCCCACCAOH. The nucleotide sequence of the other species (tRNAIle1b) is found to be the same as that of tRNAIle1a except for the modification in position 54; tRNAIle1a has s2T(54) while tRNAIle1b has T(54). The melting temperature of tRNAIle1a is as high as 86.2 degrees C while that of tRNAIle1b is 83.3 degrees C. The single replacement of an oxygen atom (2-carbonyl oxygen) of T(54) by a sulfur atom significantly contributes to the thermostability of the tRNAIle1a species. In addition, the methylation of G(18) and A(58) possibly contributes to the thermostability of T. thermophilus tRNAIle1a and tRNAIle1b species.

Base Sequence↗
PubMed1985

Volatile anesthetics cause conformational changes of bacteriorhodopsin in purple membrane.

We examined the effects of volatile anesthetics on the structure of the bacteriorhodopsin in the purple membrane by measurements of the absorption spectrum and the visible circular dichroism (CD) spectrum and assay of the retinal composition. As the concentrations of halothane, enflurane and methoxyflurane were increased, the absorption at 560 nm decreased but that at 480 nm increased with an isosbestic point around 510 nm. These anesthetic-induced spectroscopic changes were reversible. The CD spectrum showed the biphasic pattern with a positive and a negative band. As the concentration of halothane was increased from 4 mM to 8mM, the negative band reversibly diminished more drastically than the positive band, and at 8 mM of halothane the positive band shifted to around 480 nm. These results show that halothane disturbed the exciton coupling among bacteriorhodopsin molecules. The retinal isomer composition was analyzed using high performance liquid chromatography. The ratio of 13-cis- to all-trans-retinal was 47:53, 34:66 and 19:81 at control, 7.4 mM and 14.9 mM enflurane, respectively. After elimination of enflurane, the ratio returned to the control value. These findings indicate that volatile anesthetic directly affect a bacteriorhodopsin in the purple membrane and induce conformational changes in it.

Anesthetics↗
PubMed1985

15N-labeled Escherichia coli tRNAfMet, tRNAGlu, tRNATyr, and tRNAPhe. Double resonance and two-dimensional NMR of N1-labeled pseudouridine.

The N1 imino units in Escherichia coli tRNAfMet, tRNAGlu, tRNAPhe, and tRNATyr were studied by 1H-15N NMR using three different techniques to suppress signals of protons not attached to 15N. Two of the procedures, Fourier internuclear difference spectroscopy and two-dimensional forbidden echo spectroscopy permitted 1H and 15N chemical shifts to be measured simultaneously at 1H sensitivity. The tRNAs were labeled by fermentation of the uracil auxotroph S phi 187 on a minimal medium containing [1-15N]uracil. 1H and 15N resonances were detected for all of the N1 psi imino units except psi 13 at the end of the dihydrouridine stem in tRNAGlu. Chemical shifts for imino units in the tRNAs were compared with "intrinsic" values in model systems. The comparisons show that the A X psi pairs at the base of the anticodon stem in E. coli tRNAPhe and tRNATyr have psi in an anti conformation. The N1 protons of psi in other locations, including psi 32 in the anticodon loop of tRNAPhe, form internal hydrogen bonds to bridging water molecules or 2'-hydroxyl groups in nearby ribose units. These interactions permit psi to stabilize the tertiary structure of a tRNA beyond what is provided by the U it replaces.

Escherichia coli↗
PubMed1985

Structure and transcription of the tRNAPro1 gene from Escherichia coli.

A 5 kbp DNA fragment containing the tRNAPro1 gene from Escherichia coli was cloned into Charon 21A phage and sequenced by the M13 DNA sequencing technique. When the cloned DNA fragment was used as a template for in vitro transcription with E. coli RNA polymerase, a tRNAPro1 precursor of 120 nucleotide residues was obtained. The tRNAPro1 gene transcribed as a single transcription unit was followed by two unusual repeating sequences, both of 108 bp. These two repeating sequences were separated by a 60 bp spacer sequence. The 5'-portion of each repeating sequence overlapped 19 bp of the 3'-terminal region of the tRNAPro1 gene just like the repeating sequences in the E. coli tRNATyr1 gene. A rho-independent termination was present in the first repeating unit.

Base Sequence↗
PubMed1985

Improvement of endoscopic and histologic findings of AA-type gastrointestinal amyloidosis by treatment with dimethyl sulfoxide and prednisolone.

We report the successful treatment of gastrointestinal amyloidosis with dimethyl sulfoxide. A 37 year-old man with adult-onset Still's disease suffered from diarrhea. Upper and lower gastrointestinal endoscopy revealed edematous mucosa, white patches, erosions and bleeding and amyloid deposits were demonstrated in biopsy specimens. After a period of 3 months dimethyl sulfoxide and prednisolone therapy, improvement in the endoscopic appearance of the gastrointestinal tract was observed. Amyloid deposits in biopsy specimens were reduced in the stomach and negative in the large intestine.

Adult↗
PubMed1985

Transpetrosal-transtentorial approach and its application in the therapy of retrochiasmatic craniopharyngiomas.

Our experience with the transpetrosal-transtentorial approach to retrochiasmatic craniopharyngiomas is herein reviewed and an operative technique is described. Excellent exposure of the retrochiasmatic and suprasellar regions is gained with a minimal retraction of the temporal lobe and cerebellum. Eight cases of retrochiasmatic craniopharyngiomas that extended into the posterior hypothalamus were operated on utilizing this approach. The operative results were excellent in five patients, good in one, and poor in one. There was one death later. The principal advantage of this technique is that it allows the hypothalamus, even in cases in which the structure is remarkably displaced upwards, the third ventricular walls in cases of the intraventricular extension of the tumor, and the inferior surface of the optic chiasma and nerves to be visualized directly and thus safely preserved.

Adolescent↗
PubMed1985

Adjuvant activity of chitin derivatives in mice and guinea-pigs.

Adjuvant activity of chitin derivatives was examined in guinea-pigs and mice. Among derivatives of chitin tested, 30 and 70% deacetylated chitin (DAC-30 and DAC-70), were active as adjuvants for the circulating-antibody formation to bacterial alpha-amylase and for the induction of delayed-type hypersensitivity to azobenzenearsonate-N-acetyl-L-tyrosine. DAC-70 enhanced the helper T cell function, the generation of alloreactive cytotoxic T lymphocytes, and the activity of natural killer cells in mice, however, it was inactive as mitogen. Other derivatives of chitin showed weaker or no adjuvant activity compared with DAC-70. Carboxymethyl-, hydroxyethyl and dihydroxypropyl-chitin showed weak mitogenic activities on normal spleen cells.

Adjuvants, Immunologic↗
PubMed1985

Tetrahymena thermophila glutamine tRNA and its gene that corresponds to UAA termination codon.

Nucleotide sequence analysis of one of several tRNA genes cloned from Tetrahymena thermophila macronuclear DNA indicated that it corresponds to a tRNA species having TTA as anticodon. Subsequently, the tRNA species corresponding to that gene was isolated and its nucleotide sequence was determined by post-labeling techniques. The nucleotide sequence was found to be pG-G-U-U-C-C-A-U-A-m2G-U-A-psi-A-G-D-G-G-D- D-A-G-U-A-C-U-G-G-G-G-A-Cm-U-Um-U-A-i6A-A-psi-C-C-C-U-U-G-A-C- m5C-U-G-G-G-U-psi-C-G-m1A-A-U-C-C-C-A-G-U-G-G-G-A-C-C-U-C-C-AOH. This tRNA sequence exactly matched the DNA sequence of the corresponding tRNA gene. The first position of anticodon is 2'-O-methyluridine (Um), forming UmUA as the anticodon, which presumably recognizes the ochre termination codon UAA. This tRNA species is aminoacylated with glutamine by a Tetrahymena crude aminoacyl tRNA synthetase fraction, suggesting that ochre termination codon is used as a glutamine codon during cytoplasmic protein synthesis in Tetrahymena.

Animals↗
PubMed1985

Molecular mechanism of codon recognition by tRNA species with modified uridine in the first position of the anticodon.

Proton NMR analyses have been made to elucidate the conformational characteristics of modified nucleotides as found in the first position of the anticodon of tRNA [derivatives of 5-methyl-2-thiouridine 5'-monophosphate (pxm5s2U) and derivatives of 5-hydroxyuridine 5'-monophosphate (pxo5U)]. In pxm5s2U, the C3'-endo form is extraordinarily more stable than the C2'-endo form for the ribose ring, because of the combined effects of the 2-thiocarbonyl group and the 5-substituent. By contrast, in pxo5U, the C2'-endo form is much more stable than the C3'-endo form, because of the interaction between the 5-substituent and the 5'-phosphate group. The enthalpy differences between the C2'-endo form and the C3'-endo form have been obtained as 1.1, -0.7, and 0.1 kcal/mol (1 cal = 4.184 J) for pxm5s2U, pxo5U, and unmodified uridine 5'-monophosphate, respectively. These findings lead to the conclusion that xm5s2U in the first position of the anticodon exclusively takes the C3'-endo form to recognize adenosine (but not uridine) as the third letter of the codon, whereas xo5U takes the C2'-endo form as well as the C3'-endo form to recognize adenosine, guanosine, and uridine as the third letter of the codon on ribosome. Accordingly, the biological significance of such modifications of uridine to xm5s2U/xo5U is in the regulation of the conformational rigidity/flexibility in the first position of the anticodon so as to guarantee the correct and efficient translation of codons in protein biosynthesis.

Anticodon↗