摘要:

The effects of landuse, fertilizer history and soil type on the quantity and isotopic quality of hydrolysable soil amino acids were examined in 3 grassland and 2 arable soils. Results showed, (i) that overall concentrations of individual amino acids were highest in the grassland soils, (ii) that ‰δ15N values of the individual amino acids differed considerably between the five soils, and (iii) that the combination of amino acid ‰δ15N values and concentrations could be used to distinguish between landuse, crop type and fertilizer history. This preliminary study indicates that the pathways of transformation of soil amino acid N are influenced by long term N inputs and that associated biological processes are reflected in differences in concentrations and ‰δ15N values of individual soil amino acids.

ISSN:1025-6016    

DOI:10.1080/10256019708036336

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256019708036337

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

For verifying catabolic states in insulin-dependent patients and dogs the method estimating urea production rates with13C and with doubly15N labeled urea, respectively, has been established. For a fast steady state of urea tracer dilution, a prime of 600 times the continuous infusion rate had to be injected. Urea was isolated from plasma samples by protein precipitation and cation exchange chromatography with a consecutive derivatization of the dried urea fraction (trimethylsilyl derivatives). The masses of the fragment ions m/z 189 (14N14N), 190 (14N15N) and 191 (15N15N) urea are monitored to estimate the [15N2]urea frequency in the overall body urea pool in mol percent excess (MPE). 1 to 15 ng of derivatized urea were measured efficiently. An excellent correlation between expected standard and measured MPE (r= 0.9977) was achieved from solutions containing 1 to 7% [15N2]urea. The interassay coefficient of variation amounted to < 10% for a [15N2]urea portion of ≥ 3%.

ISSN:1025-6016    

DOI:10.1080/10256019708036338

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Tramadol, racemic 1-(3-methoxyphenyl)-2-(dimethylaminomethyl)cyclohexane-1-ol, is an effective analgesic drug. Metabolites of tramadol described so far originate from O- and N-demethylation and are excreted in urine directly or after conjugation. A further metabolite was found in human liver microsome incubations and in the urine of volunteers after ingestion of tramadol. To elucidate the structure of the new metabolite, seven deuterated isotopomers of tramadol have been synthesized and ingested by volunteers. The mass spectra of the metabolites derived showed (i) that it was a hydroxy metabolite, (ii) that the hydroxy group was not located on the aromatic ring, the side chain, or the positions 2 and 6 of the cyclohexane ring, (iii) that the hydroxy-group was introduced to one of the the positions 3, 4 or 5 of the cyclohexane ring. The hydroxy metabolite was formed preferentially from the (-)-enantiomer, (1S,2S)-tramadol.

ISSN:1025-6016    

DOI:10.1080/10256019708036339

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Whole body protein synthesis was investigated in growing male mice which were long-time selected for high carcass protein amount (DU-6P, protein line) or for high body weight (DU-6, growth line) and in the unselected randomly bred control (DU-Ks). Six mice/line were housed singly in metabolic cages for the estimation of N balance, whole body protein synthesis (end-product method, single dose of15N-labelled amino-acid mixture), and N distribution in the body. Another six mice/line were used for the determination of the body composition. All mice had free access to a commercial stock diet (crude protein 268 g, gross energy 19 MJ/kg dry matter) and to water. Body weight of both selection lines was about twice that of control mice at the same age. Selection for high body weight resulted in higher body fat content. Scaled to the corresponding body protein pools, the protein synthesis rates of selected mice were significantly higher than in controls, but were not significantly different between both selection lines in contrast to the protein deposition rates. The higher protein accretion in the protein line in comparison to the growth line seems to be due to a combination of a lower protein breakdown and an increased protein synthesis rate.

ISSN:1025-6016    

DOI:10.1080/10256019708036340

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two novel characteristic parameters, the latency time (tlat) and the ascension time (tasc), are proposed for evaluation of non-invasive [13C]octanoic acid breath tests for assessment of the gastric emptying of solids. In breath tests performed in control subjects (n= 30) and diabetic patients (n= 100), the usefulness of these parameters was compared to conventional parameters,i.e., gastric half emptying-timet1/2,b) and lag phase (tlag,b). The proposed parameters were only loosely correlated (controls,r= 0.199; diabetics, 0.616). A strong correlation was found between the conventional parameters (controls,r= 0.891; diabetics,r= 0.962). Based on the conventional method, 36 patients were suspicious of delayed gastric emptying including 24 patients which exhibited a simultaneous delay in both parameters. Using the new parameters, a total of 46 patients were suspicious of delayed gastric emptying with 15 and 20 having isolated delay intlatandtasc, respectively. We conclude that the novel parameters may be more appropriate for examination of the different phases of gastric emptying and for evaluation of gastric emptying disturbances in diabetic patients than the parameters conventionally used for this purpose.

ISSN:1025-6016    

DOI:10.1080/10256019708036341

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256019708036342

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

D and18O distributions were investigated in Antarctic precipitation (falling snow) and in water vapour to study their dependance on season and sampling site. Long-term sampling at the former German Georg Forster Station during 1978–93 and at the Japanese Syowa Station during 1994–97 allow conclusions about the present seasonal isotopic variations in the water inflow to Antarctica. The δD and δ18O values of precipitation at these East Antarctic coastal stations were compared with corresponding data from the West Antarctic Georg von Neumayer and Halley stations. The monthly means of these long-term data sets show typical hysteresis-like seasonal patterns of isotopic composition. Significant time lags exist regarding station temperatures, while water vapour δD values do not show such hysteresis patterns. Here, half-yearly and even quarter-yearly time components were found by Fourier analysis. Attempts were made to describe the variation in δD and δ18O values of water vapour and precipitation as well as in the resulting deuterium excess by the mixed cloud isotopic model (MCIM) of Ciais and Jouzel.

ISSN:1025-6016    

DOI:10.1080/10256019708036343

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We report preliminary results of our provenance study of marble from the Telephos Frieze of the Pergamon altar. The emphasis here is on the stable isotope geochemistry of marble. The obtained δ13C values (2.4 to 3.5‰) vary insignificantly. However, the δ18O values give two clusters. The isotopically light marbles (close to −9.5‰) derive from panels 1–8 and the heavy marbles (−3.5 to −1.0‰) derive from panels 11–50. Mineralogical, petrographic and geochemical investigations (accessory minerals, grain size distribution, rare earth elements) further refined the marble characteristics. In spite of certain differences observed (grain size distributions, isotopy and contents of certain elements) for the two marble groups, the present data support a common provenance. So far, east Aegean islands and the Marmara region are favored.

ISSN:1025-6016    

DOI:10.1080/10256019708036344

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Stable isotope (13C,18O,34S) and trace element (Sr2+, Mg2+, Mn2+, Ba2+, Na+) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing limestones have provided new insights into the geochemistry of the mineral forming environment of the native sulfur deposit at Machów (SE-Poland). The carbon isotopic composition of carbonates (δ13C = −41 to −47‰vs.PDB) associated with native sulfur (δ34S = + 10 to + 15‰vs.V-CDT) relates their formation to the microbiological anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observations, ratios near seawater composition are obtained for primary aragonite, whereas the fluids were relatively enriched in dissolved calcium during the formation of primary and secondary calcites. Based on the oxygen isotope composition of the carbonates (δ18O = −3.9 to −5.9‰vs.PDB) and a secondary SrSO4(δ18O = + 20‰vs.SMOW; δ34S = + 59‰vs.V-CDT), maximum formation temperatures of 35°C (carbonates) and 47°C (celestite) are obtained, in agreement with estimates for West Ukraine sulfur ores. The sulfur isotopic composition of elemental sulfur associated with carbonates points to intense microbial reduction of sulfate derived from Miocene gypsum (δ34S ≈ + 23‰) prior to the re-oxidation of dissolved reduced sulfur species.

ISSN:1025-6016    

DOI:10.1080/10256019708036345

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor