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Biomedical subjects

Y Yamamoto

Publications and source records attributed to Y Yamamoto.

At least 19 recordsLinked to original sources
PubMed1992

Effect of substance P on respiratory rhythm and pre-inspiratory neurons in the ventrolateral structure of rostral medulla oblongata: an in vitro study.

The pre-inspiratory (Pre-I) neurons which fire in the pre- and usually also during the post-inspiratory phase are located in the ventrolateral structures of the rostral medulla. They are suggested as primary rhythm generating neurons for respiration. These have been studied in isolated brainstem-spinal cord preparations from newborn 0-5-day-old rats. We have found that application of substance P (SP) enhanced the respiratory rhythm as measured by C4 ventral root and pre-I neuronal activities. Furthermore, the effect of SP was dependent on basal respiratory rate. An increase of the Pre-I and C4 burst rate by SP was clearer when the basal respiratory rhythm was somewhat lower. Moreover, long lasting depression of respiratory rate after the application of the alpha 2-agonist clonidine was reversed by SP. On the other hand, an inhibitory effect appeared in preparations with a higher basal respiratory rate, while the Pre-I burst rate tended to increase during SP perfusion. During chemical synaptic transmission blockade by perfusion with low Ca2+, high Mg2+ solution, a pre-I burst retained or completely blocked was found to be enhanced or reactivated by SP perfusion. The results suggest a direct postsynaptic action of SP, which could strongly stimulate burst generating properties of Pre-I neurons.

Animals↗
PubMed1992

Comparison of plasma levels of lipid hydroperoxides and antioxidants in hyperlipidemic Nagase analbuminemic rats, Sprague-Dawley rats, and humans.

The levels of lipid hydroperoxides and antioxidants in plasma samples from Nagase analbuminemic rats (NAR) and control Sprague-Dawley rats (SDR) were measured in comparison with those from normal human subjects. Cholesteryl ester hydroperoxide (CE-OOH) was detected, but phosphatidylcholine hydroperoxide was not. The levels of CE-OOH and the ratios of CE-OOH/CE were found to increase significantly in the order of human < SDR < NAR, suggesting that oxidative stress increases in the same order. NAR have a significantly lower level of ascorbate and lower ratio of ubiquinol/ubiquinone concentrations than SDR. This also suggests that NAR are subject to more oxidative stress than SDR, since ascorbate and ubiquinol are the most effective plasma antioxidants against oxygen radicals.

Adult↗
PubMed1992

Molecular mechanism for ligand stabilization in the mollusc myoglobin possessing the distal Val residue.

Myoglobin extracted from the triturative stomach of Dolabella auricularia, a common mollusc found on the Japanese coast, possesses naturally occurring substitution at the distal E7 position (Val-E7) and its oxygen affinity is only slightly lower than those of the common mammalian myoglobins possessing the usual His-E7. 1H nuclear magnetic resonance studies of Dolabella met-cyano myoglobin have revealed that a guanidino NH proton of Arg-E10 is hydrogen-bonded to the Fe-bound CN-. The role of Arg-E10 as a hydrogen-bond donor for Fe-bound ligand in the present myoglobin appears to be responsible for its relatively high ligand affinity.

Animals↗
PubMed1992

An immunohistochemical study of epithelial membrane antigen, cytokeratin, and vimentin in papillary thyroid carcinoma. Recognition of lethal and favorable prognostic types.

METHODS: Immunoreactivity for epithelial membrane antigen (EMA), cytokeratin, and vimentin was investigated in 15 papillary thyroid carcinomas (PTC) with distant metastases, 25 PTC without distant metastases, and 34 occult PTC without distant metastases that were found incidentally at autopsy. RESULTS: More than 50% of the tumor cells were positive for EMA in 7 (47%) of 15 PTC with distant metastases, 0 (0%) of 25 PTC without distant metastases, and 1 (3%) of 34 occult PTC. The incidence of EMA positivity in PTC with distant metastases was significantly different from that of both PTC without distant metastases and occult PTC (P < 0.001). Cytokeratin reactivity was similar in the three groups, and almost all PTC stained strongly for cytokeratin. Concerning vimentin positivity, there were no significant differences in three groups; however, PTC with distant metastases tended to stain more weakly or focally than PTC without distant metastases or occult PTC. CONCLUSIONS: These results suggest that EMA reactivity may be a useful factor for anticipating the individual risk of distant metastasis or death from PTC at the time of initial surgical treatment.

Adolescent↗
PubMed1992

Effects of alkyl substitutions of xanthine skeleton on bronchodilation.

Structure-activity relationships in a series of 1,3,7-trialkyl-xanthine were studied with guinea pigs. Relaxant actions in the tracheal muscle were increased with alkyl chain length at the 1- and 3-positions of the xanthine skeleton, but decreased by alkylation at the 7-position. Positive chronotropic actions in the right atrium were potentiated with 3-alkyl chain length but tended to decrease with 1-alkylation and diminish by 7-substitution. Consequently, while the 1- and 3-substitutions were equally important for the tracheal smooth muscle relaxation, the substitution at the 1-position was more important than the 3-substitution for bronchoselectivity. The 7-alkylation may be significant to cancel heart stimulation. There were good correlations between the smooth muscle relaxant action and the cyclic AMP-PDE inhibitory activity in 3-substituents and the affinity for adenosine (A1) receptors in 1-, 3-, and 7-substituents. This suggests that not only the cyclic AMP-PDE inhibitory activity but also the adenosine antagonistic activity is important in the bronchodilatory effects of alkylxanthines. Among these xanthine derivatives, 1-butyl-3-propylxanthine and its 7-methylated derivative showed high bronchoselectivity in the in vitro and in vivo experiments compared to theophylline and enprofylline and may be new candidates for bronchodilator.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1992

Conformation and length of the signal sequence affect processing of secretory protein.

Processing of human lysozyme with artificially designed signal sequences was examined in an in vitro translation-translocation system and compared with their secretory capabilities in yeast. It has been shown that the conformation of the C-terminal region of the signal sequence and the length of the hydrophobic segment are important factors for efficient cleavage of the signal sequence.

Amino Acid Sequence↗
PubMed1992

Functional signal peptide reduces bilayer thickness of phosphatidylcholine liposomes.

To investigate the interaction between a signal peptide and the lipid bilayer, two kinds of peptides, L8-M5 (L8 = MRL8PLAALG, M5 = KVFER) and L14-M5 (L14 = MRL14PLAALG), were examined in membranes composed of dioleoylphosphatidylcholine (DOPC). Peptides L8 and L14 are artificially designed signal sequences, and M5 is the N-terminal five residues of human lysozyme; L8 mediated effective secretion of human lysozyme in yeast, while L14 did not [Yamamoto, Y., et al. (1987) Biochem. Biophys. Res. Commun. 149, 431-436]. DOPC liposomes incorporating L8-M5 or L14-M5 were observed by electron cryomicroscopy as pairs of concentric circles, and the separation of the bilayer was measured along the membrane. Peptide L8-M5 was found to reduce the bilayer thickness, but L14-M5 did not. CD measurements revealed that L8-M5 adopted an alpha-helical conformation with random coil in the liposome membranes and that L14-M5 adopted a more helical and less random conformation than L8-M5. Fluorescence spectroscopy using both aqueous and membranous probes revealed that L8-M5 destabilized the lipid bilayer more strongly than L14-M5. These results suggest that functional L8-M5 reduces the bilayer thickness and destabilizes the lipid bilayer and that these activities are important for signal peptide function.

Amino Acid Sequence↗
PubMed1992

Kinetic characterization of the acid-alkaline transition in Dolabella auricularia ferric myoglobin using 1H-NMR saturation transfer experiments.

The acid-alkaline transition in ferric myoglobin of the mollusc, Dolabella auricularia, exerts the changes in both the coordination and spin states of the heme iron. Slower transition rate, compared to the NMR time scale, in this myoglobin allowed the observation of separate signals arising from the two forms, and pH titration yielded a pK value of 7.8. 1H-NMR saturation transfer experiments have been successfully used not only to provide the first signal assignments for the heme methyl proton resonances of the Met-hydroxyl form of the myoglobin, but also to determine the kinetics of the transition.

Animals↗
PubMed1992

Inhibitory actions of MCI-154 on guinea-pig femoral artery and vein preparations.

In guinea-pig femoral artery and vein preparations, the effects of MCI-154 were investigated on: (1) membrane depolarizations produced by 29.6 mM [K+]0 (high-K) solution and noradrenaline (NA) and on e.j.p.s produced by perivascular nerve stimulation; (2) contractions produced by NA, high-K and perivascular nerve stimulation; and, (3) endothelium-dependent relaxation produced by acetylcholine (ACh). In both femoral artery and vein preparations, MCI-154 (up to 10(-5) M) did not change the resting membrane potential or the depolarization produced by high-K. In preparations of femoral vein but not femoral artery, MCI-154 reduced NA-induced depolarization. The contractions produced by NA and high-K were reduced by MCI-154, the former more than the latter. The actions of MCI-154 were more pronounced in the vein than in the artery. The excitatory junction potential and contractions produced by perivascular nerve stimulation in guinea-pig saphenous artery preparations were inhibited by MCI-154 (greater than 10(-7) M). ACh-induced relaxations of guinea-pig femoral artery preparations precontracted with high-K were not affected by MCI-154. It was concluded that MCI-154 is an antagonist at postjunctional alpha 2-adrenoceptors, and, at high concentrations, inhibits voltage-dependent Ca2+ influx in vascular smooth muscle cells. These actions may contribute to the hypotensive effect of this drug.

Animals↗
PubMed1992

Action of ebselen as an antioxidant against lipid peroxidation.

The action of ebselen (2-phenyl-1,2-benzoisoselenazol-3(2H)-one) as an antioxidant was studied under various conditions to clarify how it prevents oxidative damage. It did not react with diphenylpicrylhydrazyl nor did it suppress the oxidation of methyl linoleate in acetonitrile solution or in aqueous dispersions induced by free radical initiator, suggesting that ebselen does not act as a potent radical scavenging antioxidant. On the other hand, it suppressed the oxidation of methyl linoleate emulsions in aqueous dispersions induced by iron. It also suppressed the spontaneous oxidation of rat brain and liver homogenates, but it did not suppress the oxidation of these homogenates induced by a free radical initiator. It was also found that ebselen reduced the fatty acid hydroperoxides to their corresponding alcohols and this reaction was enhanced by the presence of glutathione. These results suggest that ebselen acts as an antioxidant by reducing hydroperoxides, but that it does not act as a radical-scavenging antioxidant.

Animals↗
PubMed1992

Requirement of N- and C-terminal regions for enzymatic activity of human T-cell leukemia virus type I protease.

The requirement of N- and C-terminal regions for the enzymatic activity of human T-cell leukemia virus type I (HTLV-I) protease was investigated using a series of deletion mutants. The activity was analyzed by autoprocessing of the protease itself or by processing of the gag p53 precursor. The deletional analyses indicated that Asp38-Gly152 with an additional Met-Pro sequence at the N-terminus was probably sufficient for the enzymatic activity, although the mature HTLV-I protease consists of Pro33-Leu157. A molecular model of HTLV-I protease, which was constructed by comparison with the structure of Rous sarcoma virus protease, predicted that Pro33-Leu37 and Gly143-Leu147 would form a beta-sheet. Our experimental results and the model structure suggest that (a) five amino acids in the N-terminal region (Pro33-Leu37), which are thought to be involved in the beta-sheet, are not crucial for the enzymatic activity; (b) Pro153-Leu157 is not necessary but Pro148-Gly152 is important for the enzymatic activity, in addition to Gly143-Leu147 involved in the beta-sheet.

Amino Acid Sequence↗
PubMed1992

[An experimental and clinical study of zonography of the lung by means of Fuji computed radiography].

Tomography was conducted for a basic study using a model of the bronchi, pulmonary arteries and veins. When the exposure angle of a tube was changed to 5, 10, 25, and 50 degrees, the width of tomograms became about 10, 4, 2, and 1 cm. When tomograms of exposure angles of 50 degrees and 10 degrees were compared, the former showed fragmentary bronchi, pulmonary arteries and veins, and the latter showed bronchi, pulmonary arteries and veins branching up, down and laterally on one image in one unit and over a wide area. Similar results were obtained in 10 cases of normal volunteer. When 25 cases of lung cancer at the hilum were studied clinically with respect to bronchial lesions, the tomograms with an exposure angle of 10 degrees could point out more lesions than the tomograms with an exposure angle of 50 degrees. In 13 cases (40 lesions) which were compared with the findings of bronchoscopy, the accuracy was only 25% in tomograms with an exposure angle of 50 degrees, and 65% in tomograms with an exposure angle of 10 degrees. These results indicate that tomograms with an exposure angle of 10 degrees are useful for analysis of the bronchi, pulmonary arteries and veins at the hilum of the lung.

Adenocarcinoma↗
PubMed1992

Orientation and mobility of the heme vinyl groups in myoglobins with the aid of NOE and MATDUHM NMR.

The heme vinyl substituents in a shark (Galeorhinus japonicus) myoglobin in its met-cyano form (MbCN) have been characterized by NMR and the results were compared with those of the well-studied sperm whale (Physter catodon) myoglobin. Their orientation has been inferred from NOE connectivities and the analysis of the hyperfine shifts based on the principal magnetic tensor determined by MATDUHM (Magnetic Anisotropy Tensor Orientation Determination Utilizing the Heme Methyls) [Yamamoto, Y., Nanai, N. and Chujo, R.(1990) J. Chem. Soc., Chem. Commun. 1556-1557]. It has been shown that the C3-vinyl group is oriented roughly orthogonal to the heme plane in both G. japonicus and P. catodon MbCNs at 35 degrees C and their C8-vinyl groups, on the other hand, are close to in-plane orientation. Although CO form of myoglobin (MbCO) and MbCN have been thought to be isostructural to each other, the C8-vinyl orientation for P. catodon MbCN is found to be different from the orthogonal orientation indicated in the crystal structure analysis of MbCO [Hanson, J.C. and Schoenborn, B.P. (1981) J. Mol. Biol. 153, 117-146]. Their mobility has been characterized quantitatively from the study of time-dependent NOE build-up between the selected pair of the vinyl proton resonances. It has been revealed that the heme C3- and C8-vinyl groups of approximately 1 mM G. japonicus MbCN at 45 degrees C undergo internal motion with the correlation time of 1.9 and 2.4 ns, respectively. Therefore, their oscillatory motion is faster by a factor of 4-5 compared with the protein overall tumbling. Difference in the internal mobility between the two vinyl groups in the active site of this Mb is attributed to their differential contact with the apo-protein.

Animals↗
PubMed1992

N.m.r. study on the formation and geometry of inclusion complexes of 6-O-(alpha-maltosyl)cyclomalto-hexaose and -heptaose with p-nitrophenol in aqueous solution.

The formation and molecular geometry of inclusion complexes of some branched cyclomaltaoses with p-nitrophenol in aqueous solution have been investigated by using high-resolution 1H-n.m.r. spectroscopy. 6-O-(alpha-Maltosyl)cyclomalto-hexaose and -heptaose were found to form 1:1 inclusion complexes with p-nitrophenol, and the dissociation constants for their complexes are quite similar to those for corresponding unbranched cyclomaltaose-p-nitrophenol complexes, indicating that formation of these inclusion complexes is not hampered by the maltosyl branch. From measurement of nuclear Overhauser enhancements, it was concluded that the maltosyl branch is not situated over the entrance of the cavity.

Carbohydrate Sequence↗
PubMed1992

Cloning of the phospho-beta-galactosidase gene in Escherichia coli from lactose-negative mutants of Streptococcus mutans isolated following random mutagenesis with plasmid pVA891 clone banks.

In order to mutagenize Streptococcus mutans a marker rescue plasmid, pVA891, was employed. The plasmid was ligated with Sau3AI digested chromosomal DNA fragments from S. mutans GS-5IS3 and the resultant plasmids were amplified in Escherichia coli. These plasmids were then randomly integrated into the chromosome of strain GS-5IS3 following transformation. Lactose-negative transformants were isolated as white colonies on lactose-BTR-Xgal agar plates containing erythromycin. Six lactose-negative mutants representing three different chromosomal sites of integration were isolated from about eight thousand transformants. Mutant chromosomal DNA fragments flanking the plasmids were recovered by a marker-rescue method in E. coli and exhibited phospho-beta-galactosidase activity.

Cloning, Molecular↗
PubMed1992

Methylated cytosine level in human liver DNA does not decline in aging process.

In order to ascertain a generality of the age-dependent decrease in DNA methylation level among different mammalian species, methylated cytosine contents in human liver and spleen DNA at different ages have been determined using high performance liquid chromatography (HPLC). Unexpectedly, the liver DNA revealed no appreciable decline with age while the spleen DNA showed a slight reduction. It indicates that a decrease of methylation level in genomic DNA is not a common denominator of age-related changes in mammals.

Adolescent↗
PubMed1992

Conformational rigidity of specific pyrimidine residues in tRNA arises from posttranscriptional modifications that enhance steric interaction between the base and the 2'-hydroxyl group.

In order to elucidate roles of the 2'-O-methylation of pyrimidine nucleotide residues of tRNAs, conformations of 2'-O-methyluridylyl(3'----5')uridine (UmpU), 2'-O-methyluridine 3'-monophosphate (Ump), and 2'-O-methyluridine (Um) in 2H2O solution were analyzed by one- and two-dimensional proton NMR spectroscopy and compared with those of related nucleotides and nucleoside. As for UpU and UmpU, the 2'-O-methylation was found to stabilize the C3'-endo form of the 3'-nucleotidyl unit (Up-/Ump-moiety). This stabilization of the C3'-endo form is primarily due to an intraresidue effect, since the conformation of the 5'-nucleotidyl unit (-pU moiety) was only slightly affected by the 2'-O-methylation of the 3'-nucleotide unit. In fact even for Up and Ump, the 2'-O-methylation significantly stabilizes the C3'-endo form by 0.8 kcal/.mol-1. By contrast, for nucleosides (U and Um), the C3'-endo form is slightly stabilized by 0.1 kcal/.mol-1. Accordingly, the stabilization of the C3'-endo form by the 2'-O-methylation is primarily due to the steric repulsion among the 2-carbonyl group, the 2'-O-methyl group and the 3'-phosphate group in the C2'-endo form. For some tRNA species, 2-thiolation of pyrimidine residues is found in positions where the 2'-O-methylation is found for other tRNA species.(ABSTRACT TRUNCATED AT 250 WORDS)

Dinucleoside Phosphates↗