ISSN:1025-6016    

DOI:10.1080/10256019908234075

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The global isotope abundance of natural organic compounds is determined by that of their precursors. A prerequisite for the formation of non-statistical intermolecular and intramolecular isotope distributions is the occurance of thermodynamic and kinetic isotope effects in irreversible and branched metabolic processes. This coincidence permits the interference of external factors like climatological conditions during biosynthesis, thus leading to corresponding modulations of isotope fractionations.

ISSN:1025-6016    

DOI:10.1080/10256019908234076

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Tracers and kinetic modelling provide the opportunity to follow the movement and to quantify the metabolic fates of biological compoundsin vivo. For studies in children and for repeated studies in adults, the use of stable isotopically labelled substrates are preferable and safe. Measurement of isotopic enrichment in biological molecules is highly specific and can be extremely precise. This allows the development of models of biological system dynamics in cells and organs that are otherwise inaccessible for sampling. Applications in biochemistry, nutrition and clinical medicine show the potential of stable isotopesin vivo. Methodology is of paramount importance and includes the choice of bolus studies, (primed) continuous infusions, use of multiple tracers and use of isotopomer information and intrinsic labels. There is no limit to the number and kind of compounds that can be traced. Topics include intermediate metabolism (lipids, proteins and carbohydrates) using hydrogen, carbon and nitrogen labels. In clinical medicine,13C-breath tests are available for detection ofHelicobacter pylori([13C]urea breath test), and for assessment of a variety of gastro-intestinal and hepatic functions (e.g.[13C]octanoate and mixed [13C]triglyceride breath tests for studies of gastric emptying and fat absorption, respectively). Because theoretical, methodological, physiological and practical aspects are intertwined,in vivoresearch with stable isotopes demands close collaboration between the clinical researcher and the chemist responsible for the mass spectrometry.

ISSN:1025-6016    

DOI:10.1080/10256019908234077

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The stable isotopic geochemistry of the sulfur and carbon cycles in a modern karst environment at the southwest border of the Harz Mountains (Germany) has been studied during a 7-year period. Beside major, minor and trace elements, river and sulfate-carbonate ground water were analyzed for the13C/12C ratios of the dissolved carbonate species, the18O/16O ratio of water, and the34S/32S and18O/16O ratios of dissolved sulfate. Additionally, the carbon, sulfur and oxygen isotopic composition of the major karst aquifers (carbonate and gypsum anhydrite rocks) of the Permian Zechstein formation was measured. Nowadays, the stable isotope biogeochemistry of the river and karst water in the studied area results from the complex interactions between dissolution of biogenic CO2in the water-unsaturated zone, (minor) subterrestrial microbial decomposition reactions of organic matter (recent DOC or fossil organic matter), interactions with carbonate and sulfate aquifer minerals, and input of acids from atmospheric pollution (e.g., sulfuric acid). Subsurface precipitation of secondary calcite due to the incongruent dissolution of gypsum and/or dolomite is deduced from the hydrogeochemical composition of selected ground waters and the isotopical composition of calcite found in gypsum aquifer material. Spring and river waters were additionally influenced by the liberation of carbon dioxide into the Earth's atmosphere, a process which is accompanied by the preferrential desorbtion of12CO2. The sulfur isotopic composition of dissolved sulfate from ground and spring waters indicates a mixture of sulfate derived from surface waters (mainly originating from atmospheric pollution) and geogenic sulfate from the subsurface dissolution of gypsum/anhydrite of the Zechstein formation. The oxygen isotopic composition of dissolved sulfate is generally far away from the exchange equilibrium with water, but consistent with the two-component mixing model derived from the sulfur isotope ratios.

ISSN:1025-6016    

DOI:10.1080/10256019908234078

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Lake Hufeisen near Halle/Saale has been formed in an old mining pit. Its deepest part is trench shaped and filled with water of sodium chloride content. Due to the density difference strong mixing processes in this part of the water body are prevented all over the year (meromictic lake). Therefore anoxic conditions have been established and the organic matter of the lake sediments is converted to carbon dioxide and methane. Over a period of more than one year gas samples were collected from different water depths. The investigations of the chemical composition (mainly nitrogen, carbon dioxide and methane) and the carbon isotope ratios show different relationships for individual species. The results are discussed with respect to the behaviour of the gases in the water column and to the stability of the density stratification in the saline bottom water.

ISSN:1025-6016    

DOI:10.1080/10256019908234079

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

For water samples from mining lake ML 111 of the Lusatian Lignite District and surrounding aquifers δ34S(SO4−b), δ15N(NH4+), δD, and δ18O (H2O) values have been determined to asess the flow dynamic of the in- and outflow scenario. The high mineralization and acidification (pH > 2.6) of the lake water results from an intensive interaction with the surrounding dump sites and the inflow of extremely sulfate rich dump water (up to 4,100mg/1 SO4−). δ34S values range from −7‰ to + 7°CDT in the inflow aquifers. The lake water is considered to be a mixture of different water bodies. The evaporation signature in the outflow aquifer suggests that the groundwater consists of 60% lake water. The nitrogen transfer is explained by15N signature of ammonium. Sulfate reduction, perceptible in outflow and dump aquifer, cannot be proved within the mining lake by34S and hydrochemistry.

ISSN:1025-6016    

DOI:10.1080/10256019908234080

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

It is well established that legume species differ in intensity and duratio of nitrogen fixation during pod-filling. This was studied on new lines of white and blue lupins by comparing a solely nitrogen fixing and a treatment supplied with15N-labelled fertizlier at flowering in pot experiments. Nitrogen application at flowering markedly incresed seed and total dry matter and seed and total N yield in white lumpins but remained without effect in blue lupins. simply replacing nitrogen fixation. Nitrogen fixation virtually ceased with the onset of pod-filling in white lupins, causing a massive N-remobilization from vegetative plant parts. In contrast, the blue lupins fixed about 70% of total nitrogen fixation after flowering and displayed growth and net-N-assimilation of the vegetative plant parts. In both species the stems and pods especially supported seed N-filling, indicated by a low% N and a high C/N ratio at ripeness. It is concluded that pod-filling proved to be a critical stage for the seed yield in grain legumes. Exploiting differences in nitrogen fixation in this growth stage,e.g., by breeding, needs more precise knowledge about the regulation mechanisms and source-sink relations.

ISSN:1025-6016    

DOI:10.1080/10256019908234081

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Understanding the carbon (C) cycle in grassland pasture systems requires more information about the fate of decomposing dung material within the soil. In this soil lysimeter study we successfully applied the natural13C abundance labelling technique to trace dung-C within a temperate grassland soil. Dung was collected from beef steers fed on either maize (a C4plant) or perennial ryegrass (a C3plant) silages, and applied to a freely draining (C3) grassland soil. Leachates were collected from soil lysimeters (0–2.5) and (0–10 cm soil depth) to determine the organic carbon and13C content of < 0.7 μm filtered solution. Leachates were taken from (i) control, no dung added, (ii) C3dung and (iii) C4dung amended soil. Results showed that, (i) the addition of dung resulted in a tenfold increase in C lost from the lysimeters in drainage waters, (ii) up to 50% of the C present in the leachates was ‘native’ soil C and (iii) the application of dung produced a ‘priming’ effect. Further work is required to verify; (i) whether increased leaching of native C following dung application is a ‘true priming’ phenomenon, or merely the result of ‘displacement’ or ‘pool substitution’ of soil C, and (ii) the precise conditions and mechanisms under which organic amendments induce a true ‘priming’ effect in grassland and other agricultural soils.

ISSN:1025-6016    

DOI:10.1080/10256019908234082

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Only few data are available on intestinal calcium absorption from foodstuffs and composite meals in humans. The aim of the study was to compare intraindividually the calcium absorption from milk and from a breakfast with that from a pharmaceutical calcium preparation of equal calcium content. In 8 healthy volunteers between 44 and 58 years of age, the intestinal calcium absorption was measured in randomized order applying the double isotope technique from: (1) 500 ml of fresh milk (equivalent to 620 mg Ca), (2) a test meal composed of 250 g curd, 150 g yoghurt, 3 slices of pineapple, 2 breakfast rolls, 2 cups of coffee, 10 g of coffee cream, 20 g butter, 50 g jam and 20 g honey (equivalent to 580 mg Ca), and (3) a lactogluconate effervescent tablet (equivalent to 500 mg Ca). All test doses were given on an empty stomach and labelled with 20 mg44Ca. Simultaneously, 5 mg42Ca in a sterile isotonic solution were injected intravenously. The mean values of the absorbed fractions are 24.0% ± 5.4% (mean ± SD), 17.9% ± 7.1%, and 28.7% ± 9.1% for the milk, for the meal and for the tablet respectively. The data show that less calcium ist absorbed from foodstuffs as compared to a preparation of optimal bioavailability. But in this study only the difference between absorption from the milk and from the meal was statistically significant. Therefore, it is possible to obtain a sufficient calcium supply of the human body also by properly selected foodstuffs.

ISSN:1025-6016    

DOI:10.1080/10256019908234083

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Human milk oligosaccharides seem to play an important role in the infant's defense against bacterial and viral infections of the gastrointestinal and the urogenital tract. In this study, we investigated the influence of dietary carbohydrates on the biosynthesis of lactose and oligosaccharides in the human mammary gland and their renal excretion by the human milk-fed infant. For this purpose, a lactating woman was given 27 g galactose (Gal) containing 2 g [13C] Gal (1-13C/99%) immediately after breakfast. In the following 36 h. milk (5–10 ml) was collected before each nursing. Infant's urine was collected over a period of 24 h.13C-enrichment was measured in total milk, milk fat and protein, in the carbohydrate fraction as well as in urine by isotope ratio mass spectrometry (IRMS). Milk carbohydrates and deproteinized urine samples were fractionated by Sephadex G25 gel nitration and further analyzed by IRMS, high performance thin layer chromatography and and high pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). IRMS revealed that in milk a maximal δ13CPDBwas reached within 8h after Gal intake which then rapidly declined in the following 8h. The cumulative13C-elimination over this first peak was 6.9% of the oral13C-dose. The highest13C-enrichment was detectable in the carbohydrate fraction, mainly in lactose and neutral oligosaccharides. Compared to the enrichment of human milk, the δ13CPDBof infant's urine was delayed. In urine, the highest amount of13C was found in the Sephadex G25 fractions which mainly contained lactose, fucosyl-lactose, lacto-N-tetraose (LNT), fucosyl-LNT and difucosyl-LNT. For further characterization, individual components were separated by HPAEC-PAD and subsequently analyzed by fast atom bombardment mass spectrometry and IRMS. The data show, that orally applied Gal is incorporated in milk, especially in lactose and neutral oligosaccharides. Obviously, some of these components were absorbed by the infant and then excreted with urine. There, oligosaccharides may serve as analogous receptors for bacterial or viral adhesion molecules, and, hence, may prevent urogenital infections in breastfed infants.

ISSN:1025-6016    

DOI:10.1080/10256019908234084

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor