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Biomedical subjects

S Yamaguchi

Publications and source records attributed to S Yamaguchi.

At least 235 records · Page 13Linked to original sources
PubMed2000

Umami and food palatability.

Umami is the term that identifies the taste of substances such as L-glutamate salts, which were discovered by Ikeda in 1908. Umami is an important taste element in natural foods; it is the main taste in the Japanese stock "dashi," and in bouillon and other stocks in the West. The umami taste has characteristic qualities that differentiate it from other tastes, including a taste-enhancing synergism between two umami compounds, L-glutamate and 5'-ribonucleotides, and a prolonged aftertaste. The key qualitative and quantitative features of umami are reviewed in this paper. The continued study of the umami taste will help to further our general understanding of the taste process and improve our knowledge of how the taste properties of foods contribute to appropriate food selection and good nutrition.

Drug Synergism↗
PubMed2000

Irreversible conformational change of bacterio-opsin induced by binding of retinal during its reconstitution to bacteriorhodopsin, as studied by (13)C NMR.

We compared (13)C NMR spectra of [3-(13)C]Ala- and [1-(13)C]Val-labeled bacterio-opsin (bO), produced either by bleaching bR with hydroxylamine or from a retinal-deficient strain, with those of bacteriorhodopsin (bR), in order to gain insight into the conformational changes of the protein backbone that lead to correct folding after retinal is added to bO. The observed (13)C NMR spectrum of bO produced by bleaching is not greatly different from that of bR, except for the presence of suppressed or decreased peak-intensities. From careful evaluation of the intensity differences between cross polarization magic angle spinning (CP-MAS) and dipolar decoupled-magic angle spinning (DD-MAS) spectra, it appears that the reduced peak-intensities arise from reduced efficiency of cross polarization or interference of internal motions with proton decoupling frequencies. In particular, the E-F and F-G loops and some transmembrane helices of the bleached bO have acquired internal motions whose frequencies interfere with proton decoupling frequencies. In contrast, the protein backbone of the bO from the retinal-negative cells is incompletely folded. Although it contains mainly a-helices, its very broad (13)C NMR signals indicate that its tertiary structure is different from bR. Importantly, this changed structure is identical in form to that of bleached bO from wild-type bR after it was regenerated with retinal in vitro, and bleached with hydroxylamine. We conclude that the binding of retinal is essential for the correct folding of bR after it is inserted in vitro into the lipid bilayer, and the final folded state does not revert to the partially folded form upon removal of the retinal.

Amino Acid Sequence↗
PubMed2000

Stress-induced factor involved in flower formation of Lemna is an alpha-ketol derivative of linolenic acid.

A stress-induced substance(s) (factor C) incubated with norepinephrine (NE) has strong flower-inducing activity in Lemna paucicostata. We isolated an essential component (FIF) of factor C, and clarified its chemical structure as 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid, an alpha-ketol derivative of linolenic acid, which is formed via 9-hydroperoxy linolenic acid. Synthesized FIF showed flower-inducing activity after incubation with NE (factor C activity) equivalent to that formed in the stressed Lemna. Jasmonic acid and 13-hydroxy-12-oxo-9(Z),15(Z)-octadecadienoic acid (12,13-alpha-ketol linolenic acid), both of which are formed via 13-hydroperoxide of linolenic acid and all other derivatives of FIF synthesized by chemical and enzymatic processes failed to show the factor C activity. These results suggest that the molecular structure of FIF is very specific for the factor C activity.

Fatty Acids, Unsaturated↗
PubMed2000

Gibberellin biosynthesis: its regulation by endogenous and environmental signals.

The hormone gibberellin (GA) plays an essential role in many aspects of plant growth and development, such as seed germination, stem elongation and flower development. In recent years, exciting progress has been made in understanding how the biosynthesis of this hormone is regulated by endogenous and environmental factors. This has resulted from isolation of genes encoding enzymes involved in GA biosynthesis and metabolism, which also enabled us to manipulate the pathway by modifying the expression of these genes in transgenic plants. In addition, new GA response mutants provided information about how signaling components are involved in feedback regulation of the GA biosynthetic pathway.

Environment↗
PubMed2000

A novel protein-deamidating enzyme from Chryseobacterium proteolyticum sp. nov., a newly isolated bacterium from soil.

A novel protein-deamidating enzyme, which has potential for industrial applications, was purified from the culture supernatant of Chryseobacterium proteolyticum strain 9670(T) isolated from rice field soil in Tsukuba, Japan. The deamidating activities on carboxybenzoxy (Cbz)-Gln-Gly and caseins and protease activity were produced synchronously by the isolate. Both deamidating activities were eluted as identical peaks separated from several proteases by phenyl-Sepharose chromatography of the culture supernatant. The enzyme catalyzed the deamidation of native caseins with no protease and transglutaminase activities. Phenotypic characterization and DNA analyses of the isolate were performed to determine its taxonomy. Physiological and biochemical characteristics, 16S rRNA gene sequence analysis, and DNA-DNA relatedness data indicated that the isolate should be placed as a new species belonging to the genus Chryseobacterium. The isolate showed no growth on MacConkey agar and produced acid from sucrose. The levels of DNA-DNA relatedness between the isolate and other related strains were less than 17%. The name Chryseobacterium proteolyticum is proposed for the new species; strain 9670 is the type strain (=FERM P-17664).

Amidohydrolases↗
PubMed2000

Interaction between FliE and FlgB, a proximal rod component of the flagellar basal body of Salmonella.

FliE is a flagellar basal body protein of Salmonella whose detailed location and function have not been established. A mutant allele of fliE, which caused extremely poor flagellation and swarming, generated extragenic suppressors, all of which mapped to flgB, one of four genes encoding the basal body rod; the fliE flgB pseudorevertants were better flagellated and swarmed better than the fliE parent, especially when the temperature was reduced from 37 to 30 degrees C. Motility of the pseudorevertants in liquid culture was markedly better than motility on swarm plates; we interpret this to mean that reduced flagellation is less deleterious at low viscous loads. Overproduction of the mutant FliE protein improved the motility of the parental fliE mutant and its pseudorevertants, though not to wild-type levels. Overproduction of suppressor FlgB (but not wild-type FlgB) in the fliE mutant also resulted in improved motility. The second-site FlgB mutation by itself had no phenotype; cells swarmed as well as wild-type cells. When overproduced, wild-type FliE was dominant over FliE-V99G, but the reverse was not true; that is, overproduced FliE-V99G was not negatively dominant over wild-type FliE. We conclude that the mutant protein has reduced probability of assembly but, if assembled, functions relatively well. Export of the flagellar protein FlgD, which is known to be FliE dependent, was severely impaired by the FliE-V99G mutation but was significantly improved in the suppressor strains. The FliE mutation, V99G, was close to the C terminus of the 104-amino-acid sequence; the suppressing mutations in FlgB were all either G119E or G129D, close to the C terminus of its 138-amino-acid sequence. Affinity blotting experiments between FliE as probe and various basal body proteins as targets and vice versa revealed strong interactions between FliE and FlgB; much weaker interactions between FliE and other rod proteins were observed and probably derive from the known similarities among these proteins. We suggest that FliE subunits constitute a junction zone between the MS ring and the rod and also that the proximal rod structure consists of FlgB subunits.

Bacterial Proteins↗
PubMed2000

The flagellar hook protein, FlgE, of Salmonella enterica serovar typhimurium is posttranscriptionally regulated in response to the stage of flagellar assembly.

We investigated the posttranscriptional regulation of flgE, a class 2 gene that encodes the hook subunit protein of the flagella. RNase protection assays demonstrated that the flgE gene was transcribed at comparable levels in numerous strains defective in known steps of flagellar assembly. However, Western analyses of these strains demonstrated substantial differences in FlgE protein levels. Although wild-type FlgE levels were observed in strains with deletions of genes encoding components of the switch complex and the flagellum-specific secretion apparatus, no protein was detected in a strain with deletions of the rod, ring, and hook-associated proteins. To determine whether FlgE levels were affected by the stage of hook-basal-body assembly, Western analysis was performed on strains with mutations at individual loci encompassed by the deletion. FlgE protein was undetectable in rod mutants, intermediate in ring mutants, and wild type in hook-associated protein mutants. The lack of negative regulation in switch complex and flagellum-specific secretion apparatus deletion mutants blocked for flagellar construction prior to rod assembly suggests that these structures play a role in the negative regulation of FlgE. Quantitative Western analyses of numerous flagellar mutants indicate that FlgE levels reflect the stage at which flagellar assembly is blocked. These data provide evidence for negative posttranscriptional regulation of FlgE in response to the stage of flagellar assembly.

Bacterial Proteins↗
PubMed2000

Role of FliJ in flagellar protein export in Salmonella.

We isolated and characterized spontaneous mutants with defects in the 147-amino-acid Salmonella protein FliJ, which is a cytoplasmic component of the type III flagellar export apparatus. These mutants, including ones with null mutations, have the ability to form swarms on motility agar plates after prolonged incubation at 30 degrees C; i.e., they display a leaky motile phenotype. One mutant, SJW277, which formed significantly bigger swarms than the others, encoded only the N-terminal 73 amino acids of FliJ, one-half of the protein. At 30 degrees C, overproduction of this mutant protein improved, to wild-type levels, both motility and the ability to export both rod/hook-type (FlgD; hook capping protein) and filament-type (FliC; flagellin) substrates. At 42 degrees C, however, export was inhibited, indicating that the mutant FliJ protein was temperature sensitive. Taking advantage of this, we performed temperature upshift experiments, which demonstrated that FliJ is directly required for the export of FliC. Co-overproduction of FliJ and either of two export substrates, FliE or FlgG, hindered their aggregation in the cytoplasm. We conclude that FliJ is a general component of the flagellar export apparatus and has a chaperone-like activity for both rod/hook-type and filament-type substrates.

Amino Acid Substitution↗
PubMed2000

Avian nephritis virus (ANV) as a new member of the family Astroviridae and construction of infectious ANV cDNA.

The complete RNA genome of the avian nephritis virus (ANV) associated with acute nephritis in chickens has been molecularly cloned and sequenced. Excluding the poly(A) tail, the genome comprises 6,927 nucleotides and contains three sequential open reading frames (ORFs). The first ORF (ORF 1a) contains a sequence encoding a serine protease motif, and the second ORF (ORF 1b) has a sequence encoding an RNA-dependent RNA polymerase. ORF 1a may be linked to the second ORF by a ribosomal frameshifting mechanism. The third ORF (ORF 2) may encode the virion structural proteins as a polyprotein precursor. Two RNAs, probably genonic and subgenonic RNA (7.5 and 3.0 kb), were detected in the cytoplasm of ANV-infected cells. ANV and human astroviruses have the same genonic organization, and both are characterized by the presence of two RNA bands. The amino acid homologies of the products of ORF 1a, 1b, and 2 were 20.3, 41.9, and 25.8% to products of the corresponding ORFs of human astrovirus serotype 1 (A/88 Newcastle strain). We have constructed a genonic-length cDNA clone of ANV to test whether the in vitro transcript is infectious. When a chicken kidney cell culture was transfected with RNA transcribed in vitro and the cDNA clone, infectious virus was produced with cytopathic effects in the absence of trypsin. These observations suggested that the ANV (G-4260 strain) is a new genus of the family Astroviridae.

Animals↗
PubMed2000

Role of DBP in the circadian oscillatory mechanism.

Transcript levels of DBP, a member of the PAR leucine zipper transcription factor family, exhibit a robust rhythm in suprachiasmatic nuclei, the mammalian circadian center. Here we report that DBP is able to activate the promoter of a putative clock oscillating gene, mPer1, by directly binding to the mPer1 promoter. The mPer1 promoter is cooperatively activated by DBP and CLOCK-BMAL1. On the other hand, dbp transcription is activated by CLOCK-BMAL1 through E-boxes and inhibited by the mPER and mCRY proteins, as is the case for mPer1. Thus, a clock-controlled dbp gene may play an important role in central clock oscillation.

ARNTL Transcription Factors↗
PubMed2000

Nitric oxide enhances expression and shedding of tumor necrosis factor receptor I (p55) in endothelial cells.

The biological actions of tumor necrosis factor-alpha (TNF-alpha) are mediated by 2 distinct receptors, TNF-RI (p55) and TNF-RII (p75). The extracellular domains of both receptors are shed in soluble form (sTNF-RI and sTNF-RII). The soluble receptors are involved in regulating TNF-alpha activities and may have therapeutic potential as TNF-neutralizing agents. However, it remains unclear as to what kind of physiological molecule can regulate TNF receptors. Nitric oxide (NO) mediates a variety of biological and pathophysiological functions. We hypothesized that NO may modulate the expression and shedding of TNF-RI. An NO donor, diethylamine/NO complex (NOC 5), increased sTNF-RI in the supernatants of ECV304, a human umbilical vein cell line, in a dose-dependent manner. TNF-RI mRNA in these cells was upregulated by NOC 5. 8-Br-cGMP and peroxynitrate had no effect on sTNF-RI release. Genistein and herbimycin A, inhibitors of tyrosine kinase, inhibited sTNF-RI release. Herbimycin A inhibited the levels of TNF-RI mRNA enhanced by NOC 5, which downregulated the surface expression of TNF-RI, indicating that NO is also involved in the shedding process of TNF-RI. The shedding of TNF-RI was abolished by a synthetic inhibitor of matrix metalloproteinase, KB-R8301. In conclusion, NO enhanced the release of sTNF-RI from endothelial cells by a cGMP-independent mechanism. Dual pathways suggested for NO-induced sTNF-RI release include (1) enhanced expression of TNF-RI, at least partially, by a tyrosine kinase-dependent mechanism and (2) increased shedding of TNF-RI by a type of metalloproteinase.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2000

Inhibition of in vitro fertilization of mouse gametes by sulfated sialic acid polymers.

The effect of sialic acid (N-acetyl neuraminic acid), sialic acid dimer, sialic acid polymers (colominic acid) and sulfated colominic acid on the activity of hyaluronidase, on the dispersion of cumulus cells by mouse sperm and on in vitro mouse fertilization (sperm penetration of zona pellucida) were evaluated. Bovine testicular hyaluronidase activity was significantly inhibited by colominic acid and sulfated colominic acid, but not by sialic acid and its dimer. The dispersion of cumulus cells from eggs by mouse sperm was also inhibited by colominic acid and sulfated colominic acid. In vitro fertilization of mouse gametes was inhibited by sulfated colominic acid. The IC50 value of sulfated colominic acid-induced inhibition of fertilization was 0.3 mg/ml (ca. 0.9 mM). The value changed from 0.9 mM for cumulus-surrounded egg to 1.5 mM for cumulus free-egg. On the other hand, colominic acid showed little or no inhibitory effect on mouse in vitro fertilization at 0.5 mg/ml (ca. 1.6 mM). This antifertility activity by sulfated colominic acid did not appear to be due to an effect on sperm motility or on the oocytes. These results suggest that (1) the cumulus cells surrounding the eggs were dispersed by sperm hyaluronidase, (2) hyaluronidase was inhibited by colominic acid and by sulfated colominic acid, (3) sulfated colominic acid inhibits sperm penetration of zona pellucida by the inhibition of hyaluronidase and/or some enzymes required for mouse gametes fertilization.

Animals↗
PubMed2000

An adult case of mumps brainstem encephalitis.

We present an adult case of mumps brainstem encephalitis. He was successfully treated with steroid pulse therapy and recovered completely except for persistent dysuria. He had not been vaccinated and had no history of acute mumps infection. We consider that encephalitis in this case was caused by a reversible autoimmune process triggered by mumps infection. We emphasize the usefulness of pulse therapy for the treatment of some cases of mumps brainstem encephalitis in addition to the importance of mumps vaccination to prevent such a severe complication as encephalitis.

Adult↗
PubMed2000

Cerebral blood flow and cessation of cigarette smoking in healthy volunteers.

OBJECTIVE: The mechanisms by which cessation of cigarette smoking may improve regional cerebral blood flow (rCBF) and the details of the possible relationship remain unclear. Xenon-133 inhalation was used to determine rCBF in six smokers at baseline (during smoking) and again 6 and 9 years after they had quit smoking (quitter group). A control group of eight nonsmokers (nonsmokers group) underwent similar serial determinations. RESULTS: Regional CBF in quitters had decreased significantly after the 6 years, but improved significantly after 9 years, when abstinence had been maintained from 4 to 6 years. In the nonsmokers group rCBF did not change significantly over 9 years. CONCLUSION: Cessation of cigarette smoking improves cerebral circulation, but this effect requires several years.

Aged↗
PubMed2000

[A six year follow-up study on the influence of silent ischemic brain lesions on cognitive function and brain atrophy in elderly people].

METHODS: To investigate the influence of silent ischemic brain lesions (silent brain infarction (SBI) and periventricular hyperintensity (PVH) on cognitive function and brain atrophy, we studied MRI and cognitive tests in 27 healthy elderly people (above 65 years old) for 6 years. We examined Okabe's Scale for verbal intelligence, Koh's Block Design Test for performance intelligence and Zung's Self-rating Depression Scale (SDS). On MRI, lesions with high intensity on T2-weighted image and low intensity on T1-weighted image, and which were larger than 3 mm were diagnosed as SBI. The PVH was classified into 5 grades (0-4), and we divided the subjects into the PVH 0-1 group and the PVH 2-4 group. We evaluated brain atrophy using the ventricular area index (VAI) (the ratio of ventricular area to intracranial area at the level of lateral ventricle) on MRI by NIH image 1.55 (Macintosh). RESULTS: The SBI group and the PVH 2-4 group showed significant decline in Okabe's Score, and Koh's IQ, increase in SDS and VAI during six years. On the other hand, the non-SBI and the PVH 0-1 group showed a decline only in Okabe's score, and an increase in VAI. The rate of change in VAI was significantly higher in the subjects with SBI than those without it. However, there was no significant difference in the VAI change rate between the PVH 2-4 group and the PVH 0-1 group. CONCLUSION: Silent ischemic brain lesions such as SBI and PVH may have significant influence on decline of cognitive functions and progression of brain atrophy even in healthy elderly people.

Aged↗