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O Gabriel

Publications and source records attributed to O Gabriel.

At least 19 recordsLinked to original sources
PubMed2005

Lessons learned from investigations on case study level for modelling of nutrient emissions in the Danube basin.

In the framework of the project daNUbs (Nutrient Management in the Danube Basin and its Impact on the Black Sea) the MONERIS emission model is used for the basin wide calculation of nutrient (nitrogen and phosphorus) emissions in the Danube Basin. The MONERIS model was developed and successfully applied for German river catchments. Based on investigations in selected test regions (case studies) the daNUbs approach is to check the applicability of the MONERIS emission model for the specific conditions of the Danube Basin in more detail than is possible with a basin wide application. Six case studies with areas of 400-3,500 km2 and several subcatchments have been selected in order to represent different conditions along the Danube Basin. In this study region intensive data collection and enhanced monitoring has been performed in order to raise the database significantly above the generally available data. Water balance as well as nutrient balance calculations have been performed with the MONERIS model as well as with other approaches. Results are compared to each other and to data from monitoring. Results up till now showed the applicability and sensitivity of the MONERIS approach in different conditions of the Danube Basin (e.g. emissions via groundwater). They indicated that the nitrogen retention in the catchments is well described with the MONERIS model.

Environmental Monitoring↗
PubMed2005

Nitrogen fluxes on catchment scale: the influence of hydrological aspects.

In two catchment areas with altogether eight subcatchments characterising different site-specific situations the interaction between anthropogenic activities (e.g. agriculture, nutrition and waste water management), nitrogen emissions and in stream loads as well as concentrations were studied in detail. Groundwater is the most important pathway for nitrogen inputs into surface waters. Denitrification in the soil/subsurface/groundwater system controls the amount of this input to a high extent. Key factors influencing this process are organic carbon availability, geology, precipitation and groundwater recharge rates as well as residence time in groundwater. The MONERIS emission model is a useful tool to quantify these relationships on (sub-)catchment scale. Areas where concentrations in groundwater (e.g. nitrate) tend to be higher due to little dilution with water and might be problematic in respect to limit values for drinking water, are much less relevant in respect to the loads transported to river systems and receiving seas, than regions with high precipitation. In cases with high water availability mainly high loads transported downstream and finally to the receiving sea are a considerable problem. Within a region mainly areas close to river systems contribute to nitrogen discharges to the river system because of the short residence times of the groundwater from these areas and--related to this--a lower influence of denitrification in the groundwater.

Agriculture↗
PubMed1999

[Occult fibrin production during surgery in cyanotic congenital heart defects and extracorporeal circulation].

In 10 patients with complex cyanotic congenital defects detailed coagulation examinations were made at the beginning and end of the extracorporeal circulation after neutralization of heparin by protamine and the results were compared with a control examination, made before general heparinization, after introduction into general anaesthesia. The authors examined the activated period of blood (ACT) by means of testing tubes with a celite activator (Hemochron) as well as the HR-ACT test with a kaolin activator (Medtronic) for comparison of the results. The authors assessed quantitatively plasma levels of heparin, antithrombin III and fibrinopeptide A which is a sensitive indicator of intravascular coagulation. They assessed also the fibrinogen level and total number of thrombocytes in the blood stream. The degree of haemodilution was recorded as well as the temperature at the periods of assessment. The values of both ACT test were within the range of values above 420 secs., evaluated according to the authors protocol as adequate for total heparinization during operations under conditions of extracorporeal circulation. Despite of this heparin levels lower than those recommended in the literature were found, as well as reduced antithrombin III levels during extracorporeal circulation and a rise of fibronopeptide A levels at the end of extracorporeal circulation which suggest latent fibrin production in the patients. Laboratory results were compared with clinical symptoms of post-operation bleeding. In 50% patients after surgery signs of increased haemorrhage in the surgical field and from thoracic drains were observed, in two patients the surgical wound had to be revised. Laboratory tests revealed in two patients thrombocytopenia after surgery, one patient had a prothrombin test reduced below 45% and in one patient there was a significantly reduced fibrinogen level calling for supplementation of this factor. After improvement of the laboratory results and surgical treatment haemostasis returned to normal. All patients survived the operation and were discharged from hospital to domestic treatment.

Adolescent↗
PubMed1994

alpha 2-8 Sialic acid polymers: size, structure, and compositional analysis.

A series of three variable assay procedures is described to provide overlapping information on the size, structure, and composition of the alpha 2-8 linked polysialic acid chains present on a wide variety of critical cell surface glycoproteins. Technical advances in instrumentation have permitted the development of new applications for a methodology involving the sequential use of periodate and borohydride to modify terminal sialic acid residues. The procedures described here provide a rapid and facile assay for (a) the determination of polysialic acid chain length, (b) the simultaneous identification of N-acetylneuraminic acid, N-glycolyneuraminic acid, and KDN (deaminated sialic acid) when present in a single preparation, (c) the ability to distinguish qualitatively between reducing and nonreducing polymers, and (d) the ability to determine the number of chains bound to a glycoprotein of known molecular weight.

Carbohydrate Conformation↗
PubMed1992

Tritiated borohydride reduction of carbohydrates: reduction of individual monosaccharides, alone or in groups, results in highly divergent specific activities.

Reduction of carbohydrates by tritiated borohydride resulted in the production of alditols or glycosides with characteristically divergent specific radioactivities. Simultaneous reduction of individual sugars in the presence of a reference standard, talose, permitted the assignment of a unique specific radioactivity with respect to talitol as 100%. A variety of structures was examined, including neutral hexoses, free and acetylated aminosugars, ketohexoses and glycosides containing a fixed pyranose ring adjacent to a carbonyl group. In the latter case, the resulting steric hindrance severely restricted the incorporation of tritium. In both of the ketohexoses tested, the minor product of the two epimeric alditols exhibited the higher specific radioactivity. In all cases, reduction produced a characteristic and reproducible specific activity in which the values varied from 51 to 182% of that found for talose. These results are interpreted on the basis of generalizations concerning mechanism and predictive value.

Borohydrides↗
PubMed1985

Factors affecting binding of galacto ligands to Actinomyces viscosus lectin.

The specificity requirements for the binding of Actinomyces viscosus T14V were examined by testing simple sugars, oligopeptides, and glycoproteins as inhibitors of the aggregation of glycoprotein-coated latex beads and washed A. viscosus cells. Lactose was the most inhibitory simple sugar; D-fucose and D-galactose were equally inhibitory, methyl-alpha-D-fucoside was slightly less inhibitory, and L-fucose and raffinose were not inhibitory. The concentration of galactose residues required for 50% inhibition of aggregation was 15 times higher in the form of lactose than in the form of asialoglycoprotein, suggesting an enhancement of lectin binding when galactose residues are clustered. However, when the inhibitory power of bi-, tri-, and tetraantennary asialooligopeptides of alpha 1-acid glycoprotein was compared with that of equivalent concentrations of galactose in the form of lactose, the biantennary form was slightly less effective than lactose, the triantennary form was approximately as effective as lactose, and the tetraantennary form was slightly more effective than lactose. Steric interference may prevent this type of clustering from enhancing lectin binding. The O-linked asialooligopeptides of asialofetuin were 10 times more inhibitory than an equivalent concentration of galactose in the form of N-linked asialooligopeptides. Thus, galactose beta-1----3 linked to N-acetylgalactosamine exhibits greater specificity for the A. viscosus lectin than does galactose beta-1----4 linked to N-acetylglucosamine. These results, taken together with previously reported data, are consistent with a lectin of low affinity, binding enhanced by multivalency, and specificity for beta-linked galactose.

Actinomyces↗
PubMed1982

Characterization of a galactose-specific lectin from Actinomyces viscosus by a model aggregation system.

A simple model system has been developed in which lectin-mediated aggregation of glycoprotein-coated beads can be monitored by following the decrease in light scattering at 650 nm. Aggregation has been characterized with the lectin of Actinomyces viscosus T14V. Its dependence on pH, temperature, and stirring rate was examined, and the number of bacterial cells in relation to the number of latex beads resulting in optimal aggregation was established. This system has the advantage of permitting the study of a single ligand of defined structure. The ligand density was determined with radiolabeled glycoproteins. Under the conditions of the assay, ligand leakage was less than 3%, and ligands were not displaced from the beads by various proteins, glycoproteins, or by other components present in the assay mixture. Latex beads coated with asialofetuin aggregate upon the addition of A. viscosus T14V cells. By contrast, when asialofetuin was first extensively treated with purified galactose oxidase, no aggregation occurred. Only after reduction with NaBH(4) was aggregation restored, demonstrating that galactose termini of asialofetuin are essential for the binding of A. viscosus lectin. An absolute requirement for calcium was also demonstrated. Various sugars inhibited aggregation in the following order, starting with the most effective: lactose, methyl-beta-D-galactopyranoside, galactose, N-acetylgalactosamine, methyl-alpha-D-galactopyranoside. Beads coated with fimbriae from A. viscosus coaggregated with neuraminidase-treated human erythrocytes and with Streptococcus sanguis cells. In each instance the aggregation was inhibited by lactose, indicating that the A. viscosus lectin is located in the fimbriae. Cells grown under different conditions differed in their effectiveness in aggregating glycoprotein-coated beads, suggesting differences in lectin density or accessibility. Two different experimental designs were used to establish the minimum ligand density for aggregation to occur. In one type of experiment, a threshold concentration was found for asialo alpha(1)-acid glycoprotein, but not for asialofetuin. With an alternate approach in which a different population of galactose residues was exposed, a threshold phenomenon was also demonstrated for asialofetuin. The importance of structural ligand features in the aggregation assay is discussed in view of these findings.

Actinomyces↗
PubMed1979

Model studies on dental plaque formation: deoxyhexoses in Actinomyces viscosus.

A careful examination of two strains of Actinomyces viscosus, T14V (virulent) and T14AV (avirulent), revealed no qualitative or quantitative difference in 6-deoxyhexose content of their cell surface. For a further study of the role of these sugars in cell surface-related phenomena, the stereochemical configuration of deoxyhexoses of A. viscosus T14 was established by two complementary approaches. (i) Examination of the biosynthetic pathway was found to lead to the formation of both 6-deoxy-l-talose and 6-deoxy-l-mannose and showed no differences in the ability of either bacterial strain, A. viscosus T14V or T14AV, to produce the precursors of these cell wall components. The biosynthetic pathway for 6-deoxy-l-talose and 6-deoxy-l-mannose was found to originate from deoxy-thymidine diphosphate (dTDP)-d-glucose, which in turn is converted to dTDP-4-keto-6-deoxy-d-glucose. Epimerization at carbons 3 and 5 of the hexose moiety of dTDP-4-keto-6-deoxy-d-glucose is followed by stereospecific reduction with reduced nicotinamide adenine dinucleotide phosphate to yield dTDP-6-deoxy-l-talose and dTDP-6-deoxy-l-mannose. In cell-free extracts of both A. viscosus T14 and T14AV, an identical ratio of 6-deoxy-l-talose to 6-deoxy-l-mannose of 1:8 was produced. Known precursors for the d-isomers of the same 6-deoxyhexoses such as guanosine diphosphate-d-mannose and dTDP-d-mannose were not converted by A. viscosus T14 cell-free extracts. (ii) Isolation of 6-[U-(14)C]deoxytalose and 6-[U-(14)C]deoxymannose from both strains of A. viscosus T14 was carried out by growing cells in a medium containing d-[U-(14)C]glucose. Again no qualitative or quantitative difference was noticeable between the two strains when 6-deoxy-hexoses were released from whole cells or purified cell walls by acid hydrolysis. Radioactive 6-[U-(14)C]deoxytalose isolated from the cell surface was used in an isotope dilution experiment to establish the stereochemical configuration of this 6-deoxyhexose. The radioactive sugar was mixed with unlabeled standard d- or l-6-deoxyhexose, respectively, and conversion to the corresponding 1-phenylflavazole derivative was carried out. Recrystallization to constant specific activity identified the radioactive sugar isolated from A. viscosus to be the l-isomer. A facile synthesis of the rare sugars 6-deoxy-l-talose and 6-deoxy-d-talose is reported.

Actinomyces↗
PubMed1979

Neuraminidase-dependent hamagglutination of human erythrocytes by human strains of Actinomyces viscosus and Actinomyces naeslundii.

Human A, B, and O erythrocytes (RBC) were agglutinated by many human strains of Actinomyces viscosus and A. naeslundii. At 37 degrees C, these bacterium-mediated hemagglutination reactions required the action of bacterial neuraminidase upon the RBC; however, at 4 degrees C, the requirement for neuraminidase was not as striking. Bacterial cell suspensions which caused hemagglutination at 37 degrees C contained both soluble extracellular and cell-associated neuraminidase activities as shown by enzyme assays using a soluble substrate (i.e., alpha 1-acid glycoprotein). Bacterium-mediated hemagglutination occurred only in the presence of soluble neuraminidase activity, and the rate of hemagglutination could be inhibited by 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, a competitive inhibitor of purified soluble neuraminidase from A. viscosus T14V. Suspensions of bacteria which contained only cell-associated neuraminidase activity were unable to initiate hemagglutination, but they caused immediate hemagglutination when mixed with neuraminidase-treated RBC. All hemagglutination reactions were reversible in the presence of 0.02 M lactose and were abolished by heating (85 degrees C for 30 min) the actinomycete cells but not the RBC. The proposed mechanism of hemagglutination involves two sequential steps: (i) the action of neuraminidase to unmask galactose-containing receptors on the RBC and (ii) the multivalent binding of these receptors by many low-affinity lection sites on the bacterial surface.

Actinomyces↗
PubMed1978

Specific conversion of D-galactose into D-galacturonic acid residues in glycoproteins: a facile method for carbohydrate linkage-analysis.

The terminal D-galactopyranosyl residues of asialoglycopeptides isolated from human alpha1-acid glycoprotein were oxidized in nearly quantitative yield to the corresponding uronic acid residues by a two-step sequence employing D-galactose oxidase followed by treatment with Tollens reagent, Ag(NH3)+2. Mild acid hydrolysis of the oxidized glycopeptides led to the isolation of the corresponding aldobiuronic acid(s). Structural and colorimetric analysis revealed that only one aldobiuronic acid 2-amino-2-deoxy-4-O-(beta-D-galactopyranosyluronic acid)-D-glucose, was isolated from the oxidized glycopeptides of alpha1-acid glycoprotein. This method can readily distinguish between the (1 leads to 3), (1 leads to 4), and (1 leads to 6) isomers of the corresponding aldobiuronic acids.

Chemical Phenomena↗