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Biomedical subjects

G Reuter

Publications and source records attributed to G Reuter.

At least 91 records · Page 5Linked to original sources
PubMed1993

Reduction of naturally-occurring cell death by kainic acid in the retina of chicken embryos.

The development of the nervous system can be modified by the application of transmitter agonist or antagonists. Therefore, the growth of the retina in chicken embryos was studied after injection of the excitatory amino acid, kainate, during the second half of the pre-hatching period. Quantitative anatomical and biochemical investigations were undertaken. In the kainate treated animals the volume of the retina and its different layers was seen to exceed significantly those of control retinas from the 14th ontogenetic day onwards. This was accompanied by a total increase in cell number as well as DNA content on the 18th day of ontogenesis, though the mitotic activity during this period was comparable to that in the control group, and signs of degenerative processes ("rosettes") were found. Therefore, we conclude that the excitatory amino acid, kainate, reduces the naturally occurring cell death in the embryonic retina.

Animals↗
PubMed1993

Influence of phaseolotoxin on the alkaloid accumulation in Datura innoxia Mill.

In crude protein extracts of aseptically grown plantlets of Datura innoxia ornithine carbamoyltransferase was detected. The ornithine carbamoyltransferase of plant extracts was inhibited by phaseolotoxin. The level of this inhibition was dependent on the concentration of the toxin applied. Subsequent accumulation of ornithine in plant vegetative parts was observed. Phaseolotoxin influenced both the vitability and alkaloid accumulation of treated plants.

Alkaloids↗
PubMed1992

Solution conformations of GM3 gangliosides containing different sialic acid residues as revealed by NOE-based distance mapping, molecular mechanics, and molecular dynamics calculations.

The conformation of the GM3 ganglioside, Neu5Ac alpha 2-3Gal beta 1-4Glc beta 1-1 Cer, and its analogs containing the Neu5Gc or Neu4Ac5Gc residues (Gc = glycolyl, CH2OHCO) was investigated in Me2SO-d6 solution with the aid of a distance-mapping procedure based on rotating-frame NOE contacts, with hydroxyl protons being used as long-range sensors defining the distance constraints. A pronounced flexibility found for both the Neu-Gal and Gal-Glc linkages was confirmed by 1000-ps molecular dynamics simulations. Similar results, although based on a smaller number of NOE constraints, were obtained for GM3 gangliosides anchored in mixed D2O/dodecylphosphocholine-d38 micelles and for the Neu5Ac-, Neu5Gc-, and Neu5,9Ac2-sialyllactoses dissolved in D2O. No noteworthy differences in conformational behavior of the glycan chains of the three gangliosides or sialyllactoses were observed in either of the media.

Animals↗
PubMed1992

Occurrence of sialic acids in Drosophila melanogaster.

Sialylated oligosaccharides, which are cell type-specific and developmentally regulated, have been implicated in a variety of complex biological events. Their broad functional importance is reflected by their presence in a wide variety of phyla extending from Echinodermata through higher vertebrates. Here, sialic acids are detected throughout development in an insect, Drosophila. Homopolymers of alpha 2,8-linked sialic acid, polysialic acid, are developmentally regulated and only expressed during early Drosophila development.

Animals↗
PubMed1992

Use of influenza C virus for detection of 9-O-acetylated sialic acids on immobilized glycoconjugates by esterase activity.

An overlay and a solid-phase assay are presented which allow the specific detection of 9-O-acetylated sialic acids on sialoglycoconjugates immobilized on microtiter plates, nitrocellulose or separated on thin-layer chromatograms. The assay takes advantage of two different biological properties of influenza C virus, its high-affinity binding to 9-O-acetylated sialic acids and its sialate 9-O-acetylesterase that is used for detection of bound virus with fluorogenic or chromogenic substrates. Though simple and rapid, the assay is highly sensitive with a detection limit of 65 fmol 9-O-acetylated sialic acid in 9-O-acetylated ganglioside GD1a. Influenza C virus is able to bind to a wide spectrum of sialoglycoconjugates like mucins, serum glycoproteins or gangliosides containing naturally or synthetically O-acetylated sialic acids. 9-O-Acetyl-N-glycoloylneuraminic acid can also function as a high-affinity receptor determinant for influenza C virus. While the acetyl ester at the 9 position is essential for virus binding in all cases, a 4-O-acetyl group is not recognized. In addition to alpha(2.3) or alpha(2.6) bonds, 9-O-acetyl-N-acetylneuraminic acid in alpha(2.8) linkage to N-acetylneuraminic acid is also functionally active.

Acetylesterase↗
PubMed1992

Structural analysis of a novel sialic-acid-containing trisaccharide from Rhodobacter capsulatus 37b4 lipopolysaccharide.

Sialic-acid-containing lipopolysaccharides from Rhodobacter capsulatus 37b4 (S-form lipopolysaccharide), KB-1 (R-type lipopolysaccharide) and Sp 18 (deep R-type lipopolysaccharide) were investigated for the linkage and substitution of sialic acids. Methylation analysis and behaviour towards acid and enzymic hydrolysis indicated a non-reducing terminal location of sialic acids in the R-type lipopolysaccharide of strain Sp 18, whereas an internal, chain-linked location of sialic acids was found in the lipopolysaccharides of strains 37b4 and KB-1. For these latter strains, methylation analysis revealed a substitution of sialic acids by other sugars at position 7 for strain 37b4 and positions 4 and 7 for strain KB-1. In accordance with the chain-linked position of sialic acids, mild hydrolysis of R. capsulatus 37b4 lipopolysaccharide with acetic acid released a trisaccharide with sialic acid at the reducing terminus. Structural investigation of this trisaccharide by methylation analysis, 1H- and 13C-NMR spectroscopy revealed the presence of the disaccharide Gal1-6Glc at the non-reducing end, probably with an alpha-anomeric configuration of the galactose residue, i.e. melibiose, beta-glycosidically linked to position 7 of sialic acid. Therefore the structure Gal alpha 1-6Glc beta 1-7Neu5Ac is proposed for this core oligosaccharide from R. capsulatus 37b4 lipopolysaccharide.

Carbohydrate Sequence↗
PubMed1992

Position effect variegation and chromatin proteins.

Variegated phenotypes often result from chromosomal rearrangements that place euchromatic genes next to heterochromatin. In such rearrangements, the condensed structure of heterochromatin can spread into euchromatic regions, which then assume the morphology of heterochromatin and become transcriptionally inactive. In position-effect variegation (PEV) therefore, gene inactivation results from a change in chromatin structure. PEV has been intensively investigated in the fruitfly Drosophila, where the phenomenon allows a genetic dissection of chromatin components. Consequently, many genes have been identified which, when mutated, act as dominant modifiers (suppressors or enhancers) of PEV. Data available already demonstrate that genetic, molecular and developmental analysis of these genes provides an avenue to the identification of regulatory and structural chromatin components, and hence to fundamental aspects of chromosome structure and function.

Animals↗
PubMed1992

Analysis of carbohydrate composition and sialidase activity in oral secretions of patients with tumors in the upper aerodigestive tract.

Total saliva and secretions from parotid and submandibular glands of patients with carcinomas in the oral cavity, oropharynx or larynx and a control group of healthy individuals were analyzed for concentrations of glycosidically bound sugars and free N-acetylneuraminic acid as well as for sialidase activity. When compared to the data obtained for normal donors, the relative amounts of the individual monosaccharides fucose, galactose, mannose, N-acetylgalactosamine, and N-acetylglucosamine as components of glycoconjugates showed variable differences to the group of tumor patients depending on the type of secretion and the location of the tumor. The percentage of glycosidically linked N-acetylneuraminic acid, however, was always higher for the healthy donors. A significant difference was found in the amount of free sialic acid, with the exception of submandibular gland secretion from a patient with an oropharyngeal carcinoma, and sialidase activity which were increased for tumor patients, independent of the type of secretion and the location of the tumor. From these results it is concluded that free sialic acid and sialidase activity may be considered as markers for carcinomas in the upper aerodigestive tract.

Humans↗
PubMed1992

Regeneration of respiratory epithelia in the rat after free grafting.

Following free grafting of septal mucosa from the rat to the rectus abdominis muscle, the mucosal membrane was found to degenerate into a flat squamous epithelium with loss of the majority of differentiated epithelial cells. Both the goblet cells and ciliated cells regenerated from stem cells, which appear in large numbers 2 days after transplantation. Microvilli were found initially on the surfaces of developing ciliated cells and were replaced 21 days post-grafting by cilia. The number of goblet cells during regeneration at first exceeded that of the ciliated cells, but decreased with the passage of time. After 4 months there were more ciliated cells, with the respiratory epithelium now appearing no different than the initially transplanted nasal mucosa.

Abdominal Muscles↗
PubMed1992

Purification and characterization of a novel sialidase found in procyclic culture forms of Trypanosoma brucei.

A membrane-bound sialidase (EC 3.2.1.18) was found in procyclic trypomastigotes of Trypanosoma brucei. The mammalian stage bloodstream form, however, displayed no sialidase activity. This sialidase is an integral surface protein, linked to the membrane via a glycosylphosphatidylinositol anchor. After osmotic lysis and solubilization with Triton CF-54, the enzyme was purified 1900-fold by gel filtration and ion exchange chromatography. Its size, as determined by conventional and high-performance liquid gel chromatography, is 67 kDa. The sialidase is active over a broad pH and temperature range with optima at pH 6.9 and 35 degrees C, respectively. No loss of activity is observed after 4 freeze-thaw cycles. T. brucei sialidase activity is inhibited by N-(4-nitrophenyl)oxamic acid and 2-deoxy-2,3-didehydro-N-acetylneuraminic acid, the latter, however, being less effective. N-Acetylneuraminic acid shows no inhibitory effect, whereas a variety of metal ions are potent inhibitors. The sialidase is activated by di- and tricarboxylic acids, but inhibited by chloride. Relative hydrolysis rates of various sialic acid-containing compounds reveal that de-O-acetylated bovine submandibular gland mucin is the preferred substrate and that alpha(2-3)-linkages are hydrolyzed faster than alpha(2-6)-linkages.

Animals↗
PubMed1992

Binding of Plasmodium falciparum 175-kilodalton erythrocyte binding antigen and invasion of murine erythrocytes requires N-acetylneuraminic acid but not its O-acetylated form.

Sialic acid on human erythrocytes is involved in invasion by the human malaria parasite, Plasmodium falciparum. Mouse erythrocytes were used as a reagent to explore the question of whether erythrocyte sialic acid functions as a nonspecific negative charge or whether the sialic acid is a necessary structural part of the receptor for merozoites. Human erythrocytes contain N-acetylneuraminic acid (Neu5Ac), whereas mouse erythrocytes, which are also invaded by P. falciparum merozoites, contain 9-O-acetyl-N-acetylneuraminic acid (Neu5,9Ac2) and N-glycoloylneuraminic acid (Neu5Gc), in addition to Neu5Ac. We compared the effects of sialidase and influenza C virus esterase treatments of mouse erythrocytes on invasion and the binding of a 175-kDa P. falciparum protein (EBA-175), a sialic acid-dependent malaria ligand implicated in the invasion process. Sialidase-treated mouse erythrocytes were refractory to invasion by P. falciparum merozoites and failed to bind EBA-175. Influenza C virus esterase, which converts Neu5,9Ac2 to Neu5Ac, increased both invasion efficiency and EBA-175 binding to mouse erythrocytes. Thus, the parasite and EBA-175 discriminate between Neu5Ac and Neu5,9Ac2, that is, the C-9 acetyl group interferes with EBA-175 binding and invasion by P. falciparum merozoites. This indicates that sialic acid is part of a receptor for invasion.

Animals↗
PubMed1992

Culture media for enterococci and group D-streptococci.

Lancefield group D-streptococci are contaminants of various food commodities, especially those of animal origin. They encompass the new genus Enterococcus comprising 13 known species and some species of streptococci which have their habitat in the intestine of animals, e.g. Streptococcus bovis, suis and equinus. The serologically based grouping may no longer constitute the best definition for streptococci from the food chain. Food hygiene monitoring systems using enterococci as indicators need reliable methods for selective cultivation and identification of marker strains. Up to now more than 100 modifications of selective media have been described for isolating streptococci or enterococci from various specimens. The selection of a medium requires either experience or consultation. It depends on the kind of specimen, the method of cultivation (plate count or membrane filter) and whether or not the habitat is heavily contaminated with other organisms. The choice of media is made more difficult as commercial versions of the same culture medium may vary in recipe and/or performance from producer to producer. Therefore, reviewing the literature may help in the choice of medium and confirmation tests. The selectivity and productivity of some commonly used or cited media are reported here, partly based on our own experience: citrate azide tween carbonate agar (CATC), kanamycin aesculin azide agar (KAA) and M-enterococcus agar (ME) including earlier results with aesculin bile azide agar (ABA), and thallous acetate tetrazolium glucose agar (TITG). No medium was completely selective for all group D-streptococci or for all enterococci but some media were highly selective for a single Enterococcus species, e.g., for E. faecalis which serves as indicator of human pollution. Confirmatory tests must be carried out when experience in the evaluation procedure is limited. Selective media for enterococci should be used only after or while checking in parallel their selectivity and productivity against appropriate test organisms.

Animals↗
PubMed1992

Nature and biosynthesis of sialic acids in the starfish Asterias rubens. Identification of sialo-oligomers and detection of S-adenosyl-L-methionine: N-acylneuraminate 8-O-methyltransferase and CMP-N-acetylneuraminate monooxygenase activities.

Mass spectrometric and NMR spectroscopic analyses of bound sialic acids from the starfish Asterias rubens revealed the presence of N-acetylneuraminic acid (4%), N-acetyl-8-O-methylneuraminic acid (12%), N-acetyl-9-O-acetyl-8-O-methylneuraminic acid (less than 1%), N-glycoloylneuraminic acid (19%), N-glycoloyl-8-O-methylneuraminic acid (47%), and N-glycoloyl-9-O-acetyl-8-O-methylneuraminic acid (18%). Analysis of sialo-oligomeric material, obtained after mild acid hydrolysis, demonstrated that N-glycoloyl-8-O-methylneuraminic acid can occur as di- and tri-oligomers, linked through the anomeric center and the N-glycoloyl moiety, Neu5Gc8Me-alpha(2----O5)-Neu5Gc8Me and Neu5Gc8Me-alpha(2----O5)-Neu5Gc8Me-alpha (2----O5)-Neu5Gc8Me. Studies on the biosynthesis of N-acyl-8-O-methylneuraminic acid in A rubens, using the tracer S-adenosyl-L-[methyl-14C]methionine, showed that N-acylneuraminate 8-O-methyltransferase activity was present predominantly in the membrane fraction. CMP-N-acetylneuraminic acid monooxygenase activity was found in the soluble protein fraction, in agreement with investigations on the corresponding vertebrate enzyme.

Animals↗
PubMed1992

High frequency radial movements of the reticular lamina induced by outer hair cell motility.

Recently, it was shown in cochlear explants from the guinea pig cochlea that electrokinetic motile responses of outer hair cells can induce radial and transverse motion of the reticular lamina. Here we demonstrate, that the radial component of these motions can be measured up to high frequencies (15 kHz). Cochlear explants were taken from guinea pig inner ears and exposed to a sinusoidal electric field. A double photodiode was used as a linear position detector with high spatial and temporal resolution to detect radial movements in the plane of the reticular lamina. The organ of Corti of the second, third and fourth cochlear turns was stimulated with frequencies of the electrical field between 0.5 Hz and 20 kHz. Sinusoidal movements of up to 15 kHz were recorded. At higher frequencies the signal-to-noise ratio became too small. The largest responses were measured at the three rows of outer hair cells. If the strength of the electrical field was 2 kV/m, into which the cochlear explants were placed, the amplitudes of outer hair cell movements were around 1 micron at 1 Hz and 10 nm at 10 kHz. Uncoupling of the outer hair cells from the tunnel of Corti and from the inner hair cells decreased the oscillations of inner hair cells but did not affect outer hair cells. The movements showed frequency dependent amplitudes like a complex low-pass filter but no best frequency was observed.

Animals↗
PubMed1992

The heterochromatin-associated protein HP-1 is an essential protein in Drosophila with dosage-dependent effects on position-effect variegation.

Chromosome rearrangements which place euchromatic genes adjacent to a heterochromatic breakpoint frequently result in gene repression (position-effect variegation). This repression is thought to reflect the spreading of a heterochromatic structure into neighboring euchromatin. Two allelic dominant suppressors of position-effect variegation were found to contain mutations within the gene encoding the heterochromatin-specific chromosomal protein HP-1. The site of mutation for each allele is given: one converts Lys169 into a nonsense (ochre) codon, while the other is a frameshift after Ser10. In flies heterozygous for one of the mutant alleles (Su(var)2-504), a truncated HP-1 protein was detectable by Western blot analysis. An HP-1 minigene, consisting of HP-1 cDNA under the control of an Hsp70 heat-inducible promoter, was transduced into flies by P element-mediated germ line transformation. Heat-shock driven expression of this minigene results in elevated HP-1 protein level and enhancement of position-effect variegation. Levels of variegating gene expression thus appear to depend upon the level of expression of a heterochromatin-specific protein. The implications of these observations for mechanism of heterochromatic position effects and heterochromatin function are discussed.

Alleles↗
PubMed1992

Interaction of rat peritoneal macrophages with homologous sialidase-treated thrombocytes in vitro: biochemical and morphological studies. Detection of N-(O-acetyl)glycoloylneuraminic acid.

Sialidase treatment of rat thrombocytes led to an increased binding of these cells to homologous peritoneal macrophages, but had no significant effect on the rate of phagocytosis during the experimental time. As revealed by electron microscopy, the partially desialylated thrombocytes adhere to macrophages predominantly via a small part of the membrane in a way that the discoidal cells adopt a vertical position with regard to the macrophage surface. One adherent macrophage was able to bind up to 55 sialidase-treated thrombocytes. Maximum binding was already reached after release of 13% of sialic acids. This interaction could be inhibited by free D-galactose and compounds with terminal D-galactose residues. Bound thrombocytes were released from the macrophages by treatment with lactose or EDTA. These experiments suggest that the interaction is mediated by a galactose-specific receptor on the macrophage surface and that galactose on thrombocytes is not recognized if it is masked by terminal sialic acid residues. The total sialic acid amount of the thrombocytes studied was about 70 micrograms sialic acid/10(10) cells being composed of 78% N-glycoloylneuraminic acid, 17% N-acetylneuraminic acid and 5% of the novel sialic acid N-(O-acetyl)glycoloylneuraminic acid, which was identified by mass spectrometry. Sixty-two percent of these sialic acids were susceptible to enzymic hydrolysis with Vibrio cholerae sialidase.

Animals↗