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Biomedical subjects

B Keller

Publications and source records attributed to B Keller.

At least 91 records · Page 5Linked to original sources
PubMed1992

Cloning and sequence analysis of the phenylalanyl-tRNA synthetase genes (pheST) from Thermus thermophilus.

While crystals suitable for X-ray diffraction analyses are available of phenylalanyl-tRNA synthetase (PheRS) from the thermophilic bacterium Thermus thermophilus, neither the primary structure of its constituent alpha and beta subunits nor the nucleotide sequence of the corresponding pheS and pheT genes were known. Using specific oligonucleotides of conserved pheS regions that were adapted to the T. thermophilus codon usage, we identified, cloned and subsequently sequenced the pheST genes of this bacterium. The sequences reported here will greatly aid in the three-dimensional structure determination of T. thermophilus PheRS, a heterotetrameric (alpha 2 beta 2), class II aminoacyl-tRNA synthetase.

Amino Acid Sequence↗
PubMed1992

Incidence of childhood malignancies in the vicinity of west German nuclear power plants.

The incidence of childhood malignancies in 20 areas surrounding major nuclear installations is compared with the incidence in matched control regions. The study is based on the registry of childhood malignancies in the Federal Republic of Germany and includes 1,610 cases which were diagnosed before 15 years of age from 1980 to 1990. The relative risk (RR) was 0.97 for all malignancies and 1.06 for acute leukemia in all regions within a 15 km radius of an installation. Increased RR was observed in subgroups for acute leukemia before five years of age and for lymphomas, especially in regions close to installations (less than 5 km) which started operation before 1970. Most of this increase was attributable to an unexpectedly low incidence in the control regions which could not be explained by analyzing possible confounding factors. Using the same control regions, a comparable and even more pronounced increase of RRs was observed in regions where nuclear power plants have been projected.

Adolescent↗
PubMed1992

Enhancement of intestinal hydrolysis of lactose by microbial beta-galactosidase (EC 3.2.1.23) of kefir.

The effect of microbial beta-galactosidase (EC 3.2.1.23) activity on intestinal lactose digestion was estimated directly by following post-prandial venous plasma galactose concentrations. To avoid superimposing effects of free galactose, as with yogurt, fresh or heat-treated suspensions of mechanically disintegrated kefir grains in kefir, containing lactose but no free galactose, were fed to ten Göttingen minipigs. Each meal contained 101.1 (SEM 0.1) mmol lactose in kefir supplemented by either native or heat-treated kefir grains corresponding to a mean beta-galactosidase activity of either 72 (SEM 8) U or zero. Feeding kefir with beta-galactosidase activity resulted in a 30% enhancement of the mean post-prandial plasma galactose peak concentration from 33 (SEM 7) to 43 (SEM 12) mumol/l (n 10), as well as in 23% greater mean areas under the galactose-response curves (8.1 (SEM 1.5) v. 6.6 (SEM 1.2) mmol/min per l) if compared with kefir with heat-treated grains. Both differences were significant (P less than 0.05; paired Wilcoxon test by ranks). There was no induction of intestinal beta-galactosidase (EC 3.2.1.108) activity or intestinal lactose-hydrolysing bacteria by lactose feeding. These results give direct evidence of an enhanced lactose digestion and absorption in native fermented milk products due to the microbial beta-galactosidase activity.

Animals↗
PubMed1992

Bioeffects in echocardiography.

Two mechanisms have been identified through which ultrasound as it is used clinically could produce biologically significant effects. One is heating that results from the absorption of ultrasonic energy by tissues. The other is cavitation, the ultrasonic activation of gas bodies including the potentially violent collapse of small gas bodies in or near tissue that is sometimes called transient or inertial cavitation. The heart, itself, is well perfused and the likelihood of significant heating of the heart tissues in the most extreme conditions known today is negligible. Lung also appears to be relatively immune to heating under diagnostic exposure conditions. In normal echocardiographic procedures, the only tissues that need serious consideration are the ribs. Under extreme conditions, ultrasonic heating of the bone might be as great as 6 degrees C. Nonthermal action of ultrasound has been demonstrated to cause lung hemorrhage at pressure levels on the order of 1 MPa. Although many diagnostic devices produce focal pressures greater than this amount, it appears unlikely that hemorrhage will occur in normal echocardiographic applications. Under certain conditions, pulsed ultrasound can either stimulate or modify the contraction of the heart but the exposures required are not used in normal echocardiographic applications. Since specific devices have been identified who's outputs approach levels required to produce thermal and nonthermal effects, the user should be aware of potential biological effects, particularly in pediatric or obstetric applications, as output levels increase.

Animals↗
PubMed1992

Identification of the pheS5 mutation, which causes thermosensitivity of Escherichia coli mutant NP37.

The pheS5 mutation responsible for the thermosensitive phenylalanyl-tRNA synthetase of the classical Escherichia coli NP37 was cloned by a recombination event and identified by DNA sequence analysis. The mutation was subsequently verified by direct sequencing of amplified NP37 DNA generated by an asymmetric polymerase chain reaction. The resulting amino acid exchange, Gly-98 to Asp-98 in the phenylalanyl-tRNA synthetase alpha subunit, might cause subunit disaggregation due to electrostatic repulsion.

Amino Acid Sequence↗
PubMed1992

[An outbreak of infectious chicken anemia in fattening chickens in Switzerland].

An outbreak of infectious anaemia in 46 broiler flocks due to chicken anaemia agent (CAA) is described. The vertically acquired infection led to increased mortality (3.6-19.8%) in 16 to 24 day-old broiler chickens. At necropsy severe atrophy of thymus and anaemia with pale bone marrow was observed. The histologic findings were depletion of cortical thymocytes and of hematopoietic cells in the bone marrow. The CAA was isolated from 15 of 35 examined broiler flocks.

Anemia↗
PubMed1991

Action of the racemate and the isomers of the platelet-activating factor antagonist bepafant (WEB 2170) after oral administration to guinea-pigs and rats.

The aim of the present study was to clarify whether there is a difference in terms of potency and pharmacodynamic half time between the isomers and the racemate of the platelet-activating factor antagonist WEB 2170 (bepafant) after oral administration to guinea-pigs or rats. The following experiments were performed in the guinea-pig. Infusion of platelet-activating factor at 30 ng/(kg x min) for 30 min to anaesthetized guinea-pigs induced a decrease of respiratory flow and mean arterial blood pressure. Oral pretreatment with WEB 2170 or isomers, respectively, 60 min before infusion of platelet-activating factor inhibited these changes in a dose-dependent manner. The ED50s for inhibition of respiratory flow were: (-) WEB 2170 = 0.018 (0.009-0.036) mg/kg p.o; (+/-) WEB 2170 = 0.021 (0.015-0.03) mg/kg p.o.; (+) WEB 2170 = 1.55 (1.01-3.05) mg/kg p.o. Similar ED50 values were obtained for inhibition of decrease of MAP. Doses of isomers and racemate of WEB 2170 that provided almost complete protection against platelet-activating factor at 1 h after administration were chosen for determination of the duration of the protective effect after oral administration. Oral (-) WEB 2170 or (+/-) WEB 2170 showed almost identical time-response curves for inhibition (t1/2 = 14-17 h; 0.1 mg/kg p.o.) in the guinea-pig, whereas the duration of action of (+) WEB 2170 (3-6 h; 8 mg/kg) was significantly shorter. The following experiments were conducted in the rat. Oral pretreatment with WEB 2170 racemate and isomers resulted in a dose-dependent reversal of platelet-activating factor-induced hypotension.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1991

Vascular-specific expression of the bean GRP 1.8 gene is negatively regulated.

In French bean, the glycine-rich cell wall protein GRP 1.8 is specifically synthesized in the vascular tissue. To identify cis-acting sequences required for cell type-specific synthesis of GRP 1.8, expression patterns of fusion gene constructs were analyzed in transgenic tobacco. In these constructs, the uidA (beta-glucuronidase) gene was placed under control of 5' upstream deletions as well as internal deletions of the GRP 1.8 promoter. Four different cis-acting regulatory regions, SE1 and SE2 (stem elements), a negative regulatory element, and a root-specific element, were found to control the tissue-specific expression. Deletion of the negative regulatory element resulted in expression of the uidA gene in cell types other than vascular cells. The SE1 region was essential for expression in several cell types in the absence of further upstream regulatory sequences. Full-length promoters having insertions between the negative regulatory element and SE1 strongly expressed the gene in nonvascular cell types in stems and leaves. Thus, vascular-specific expression of the GRP 1.8 promoter is controlled by a complex set of positive and negative interactions between cis-acting regulatory regions. The disturbance of these interactions results in expression in additional cell types.

Base Sequence↗
PubMed1991

Morphometric analysis of compartments concerned with secretion of parathyroid hormone in male and female rats.

Parathyroid cells responded to estradiol application in rats by increment in surface area of the compartments concerned with parathyroid hormone secretion, i.e. the rough endoplasmic reticulum, Golgi complex and secretory granules. We thus compared the morphology of parathyroids of male rats with those of females of the same age and same weight, respectively. Morphometric analysis revealed that (i) the mean cell volume was significantly larger and, consequently, the number of parathyroid cells lower expressed per 1 mm3 tissue and (ii) the surface area of the Golgi complex was larger expressed per mean parathyroid cell volume and per 1 mm3 tissue in female rats than in males. Diversity in cell volume seems to depend on age rather than on sex, whereas diversity in the Golgi complex is considered to be sex related. The physiological implications remain to be clarified.

Aging↗
PubMed1991

A new method to monitor Kupffer cell phagocytosis continuously in perfused rat liver.

A new method was developed to monitor Kupffer cell phagocytosis continuously in perfused liver using a fluorescent probe, rhodamine-gelatin, synthesized from gelatin and rhodamine isothiocyanate. In perfused rat liver, phagocytosis by Kupffer cells was assessed both by uptake of the dye and from fluorescence measured from the liver surface. Uptake of rhodamine-gelatin and surface fluorescence (520----585 nm) increased as perfusate concentrations of rhodamine-gelatin were elevated. Histological examination revealed that fluorescence caused by rhodamine-gelatin was concentrated in cells lining the sinusoid. Furthermore, when hepatic parenchymal, endothelial and Kupffer cells were isolated by centrifugal elutriation after pretreatment in vivo with rhodamine-gelatin, the fluorescent label was detected nearly exclusively in the Kupffer cell fraction. Fluorescence of rhodamine-gelatin from the liver surface was directly proportional to uptake of rhodamine-gelatin, indicating that measurement of surface fluorescence could be used as an index of phagocytic activity of Kupffer cells. Uptake of rhodamine-gelatin and fluorescent labeling of sinusoidal cells were inhibited nearly completely by dextran sulfate, which decreases phagocytic activity, and were increased by about 50% by pretreatment with endotoxin, which stimulates phagocytosis. This new method was combined with standard procedures to monitor parenchymal cell function (e.g., oxygen uptake and release of lactate dehydrogenase), Kupffer cell phagocytic activity and parenchymal cell injury simultaneously during perfusion with the hepatotoxicant allyl alcohol. Activation of phagocytosis by Kupffer cells monitored by rhodamine-gelatin fluorescence occurred within 5 min of addition of allyl alcohol. On the other hand, parenchymal cell injury, assessed from release of lactate dehydrogenase, did not begin until 40 min and reached maximal values at around 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

[Pathologico-anatomic, bacteriologic and serologic findings in laying hens from small neighborhood flocks with Salmonella enteritidis phage type 4 infection].

Two small free range flocks with 32 hens, whose Salmonella enteritidis contaminated eggs caused salmonellosis in man, were investigated for localisation of the agent. Salmonella enteritidis phage type 4 was isolated from 12 of 32 hens (37.5%). Eight hens (25%) harbored the bacterium in the ovary and/or the oviduct. The rapid slide agglutination test with Salmonella pullorum-antigen revealed 21 positive hens (66%). All eight hens with Salmonella enteritidis phage type 4 in the reproductive tract were seropositive. The significance of these findings for the control of Salmonella enteritidis phage type 4-infections in poultry is discussed.

Animals↗
PubMed1990

Predictability and intraindividual variability of serum theophylline concentrations in patients with obstructive lung disease: 12-h versus 24-h dosing.

The predictability and intraindividual variability of serum theophylline concentrations (STC) after different dosing schedules were investigated in 24 patients with chronic obstructive lung disease (COLD). Three oral regimens were compared in 3 groups of 8 randomly assigned patients. Group I:Drug A once daily in the evening; Group II: Drug A b.d.; Group III: Drug B b.d. The doses for each patient were estimated by Bayesian forecasting aiming at an STC of 10-15 mg/l. STC and FEV1 were measured on two consecutive days at steady-state. The day-to-day variability of STC was less than 20% in all three groups. The within-day fluctuation in Group I amounted to 259% (median) compared to 57% and 38% in Groups II and III, respectively. Dose adjustment by Bayesian forecasting resulted in a therapeutic STC in most patients with a b.d. regimen, whereas for the once daily dose the prediction was not satisfactory. No difference in lung function was found between the 24-h and 12-h dosing, probably because of the large intersubject variability in FEV1. Therefore, the question whether the differences in STC profile are of clinical importance in COLD can only be investigated in a larger group of patients.

Adult↗
PubMed1989

Determination of the new monoamine oxidase inhibitor brofaromine and its major metabolite in biological material by gas chromatography with electron-capture detection.

A sensitive gas chromatographic assay for the simultaneous determination of brofaromine [4-(7-bromo-5-methoxy-2-benzofuranyl)piperidine hydrochloride], a new monoamine oxidase-A inhibitor, and its major metabolite was developed and validated. After addition of 4-(5-bromo-2-benzofuranyl)piperidine as internal standard, the compounds were isolated from biological fluids by liquid-liquid extraction at basic pH. After derivatization with heptafluorobutyric anhydride the compounds were chromatographed using a packed column (OV-17) and an electron-capture detector. The limit of quantitation was ca. 0.03 nmol per sample (10 ng) for both compounds. analysis of spiked samples demonstrated the good accuracy and precision of the method, which is suitable for use in pharmacokinetic and bioavailability studies. The method was applied to samples from an experiment in a healthy volunteer treated with a single oral dose of 75 mg of brofaromine hydrochloride. Plasma profiles before and after enzymic hydrolysis showed that about one-third of the total brofaromine in plasma and practically all of the major metabolite (O-desmethylbrofaromine) were present in the conjugated form.

Chemical Phenomena↗
PubMed1989

Vascular expression of a bean cell wall glycine-rich protein-beta-glucuronidase gene fusion in transgenic tobacco.

In French bean (Phaseolus vulgarisL.), the glycine-rich wall protein GRP 1.8 is specifically synthesized in protoxylem tracheary elements of the vascular system. A 494 bp upstream promoter fragment of the gene encoding GRP 1.8 was isolated and translationally fused to the beta-glucuronidase reporter gene. Transgenic tobacco plants containing this construct expressed the gene in vascular tissue of roots, stems, leaves and flowers. The gene was developmentally expressed during differentiation of both primary and secondary vascular tissue and was also rapidly induced (in < 30 min) after excision-wounding of young stems. This wound response is more rapid than in bean hypocotyls, indicating possible differences between the activation mechanism for glycine-rich protein gene expression in wounded bean and tobacco. Only a subset of cells were found to participate in the wound response. In young stems, the GRP wound induction was localized in pith parenchyma cells adjacent to the wound surface, where vessel regeneration is known to occur. Thus, a promoter fragment of 494 bp, including 427 bp upstream from the transcription start site, contains information for tissue-specific and wound-induced gene regulation. The cell-type specificity of expression suggests that the GRP 1.8 promoter is regulated by very specific developmental and environmental signals.

Journal Article↗
PubMed1989

Specific localization of a plant cell wall glycine-rich protein in protoxylem cells of the vascular system.

An antibody against glycine-rich protein 1.8 of bean (Phaseolus vulgaris L.) was used for immunogold/silver localization of the protein in different organs of the plant. In hypocotyls, ovaries, and seed coats, the protein was found specifically in xylem cells of the vascular tissue. In hypocotyls, only protoxylem cells were labeled with the antibody, which indicates a remarkable cell-type specificity for accumulation of this cell wall protein. In mature hypocotyls, the protein was restricted to the same subset of xylem cells but was no longer detected on tissue prints, where a positive antibody reaction depends on the transfer of soluble material from plant tissue to the nitrocellulose filter. This indicates that the glycine-rich protein is insolubilized in the cell wall during development. In longitudinal sections of tracheary elements of young hypocotyls and seed coats, the antibody stained a pattern very similar to that of the lignified secondary thickenings of the cell wall, which suggests a close functional relationship between glycine-rich protein and lignin deposition during cell wall biogenesis in protoxylem cells.

Journal Article↗
PubMed1989

Specific expression of a novel cell wall hydroxyproline-rich glycoprotein gene in lateral root initiation.

A gene encoding a novel cell wall hydroxyproline-rich glycoprotein (HRGPnt3) was isolated from a genomic library of tobacco. The deduced protein (620 amino acids, Mr, 65,406) contains an amino-terminal hydrophobic signal peptide, is highly basic, and is rich in proline, although characteristic Ser-Pro4 repeats are found only beyond residue 204. At the carboxyl terminus, there is a 34-amino-acid unit repeated three times. Arginine is the predominant basic amino acid rather than lysine, as in other HRGPs. A second gene homologous to HRGPnt3 was revealed by Southern blot hybridization of tobacco genomic DNA. Northern blot hybridization identified a 1.9-kb transcript present at low levels in roots. To determine the underlying spatial pattern of expression, the HRGPnt3 promoter and the first 27 nucleotides of the open reading frame were fused to the beta-glucuronidase (GUS) reporter gene and transformed back into tobacco. Histochemical localization of GUS activity showed that the HRGPnt3 promoter was transiently induced in the pericycle and endodermis, specifically in the discrete, small subset of cells involved in the initiation of lateral roots. This pattern of expression, in cells destined to form the tip of the emerging lateral root, indicates that the encoded cell wall protein has a specialized structural function, possibly in the mechanical penetration of the cortex and epidermis of the main root, and that the HRGPnt3 promoter responds to an early morphogenetic signal for lateral root induction.

Amino Acid Sequence↗