scholarly journals Human hepatic N-acetylglutamate content and N-acetylglutamate synthase activity. Determination by stable isotope dilution

1990 ◽  
Vol 271 (2) ◽  
pp. 325-329 ◽  
Author(s):  
M Tuchman ◽  
R A Holzknecht
Keyword(s):  
Stable Isotope ◽  
Isotope Dilution ◽  
Liver Tissue ◽  
Internal Standard ◽  
Tissue Homogenate ◽  
Selected Ion Monitoring ◽  
Human Liver Tissue ◽  
Stable Isotope Dilution ◽  
Acetylglutamate Synthase

N-Acetyl-L-glutamate (N-acetylglutamate) content and N-acetylglutamate synthase activity ranges were established in human liver tissue homogenates by stable isotope dilution. The methods employ N-[methyl-2H3]acetyl[15N]glutamate as internal standard, extraction of N-acetylglutamate by anion-exchange technique and its determination by g.l.c.-mass spectrometry by using selected ion monitoring. Hepatic N-acetylglutamate content in 16 different human livers, normal in structure and function, ranged from 6.8 to 59.7 nmol/g wet wt. (25.0 +/- 13.4 mean +/- S.D.) or from 64.6 to 497.6 nmol/g of protein (223.2 +/- 104.2 mean +/- S.D.). In vitro, N-acetylglutamate synthase activity in liver tissue homogenate ranged from 44.5 to 374.5 (132.0 +/- 90.6 mean +/- S.D.) nmol/min per g wet wt. or from 491.7 to 3416.9 (1159.6 +/- 751.1 mean +/- S.D.) nmol/min per g of protein. No correlation was found between hepatic N-acetylglutamate concentrations and the respective maximal enzymic activities in vitro of N-acetylglutamate synthase. The marked variability in this system among individual livers may reflect its regulatory role in ureagenesis.

scholarly journals Quantitative Analysis of 2-Aminoacetophenone in Off-Flavored Wines by Stable Isotope Dilution Assay

1996 ◽  
Vol 79 (2) ◽  
pp. 583-586 ◽  
Author(s):  
Bettina Dollmann ◽  
Dominicus Wichmann ◽  
Alfred Schmitt ◽  
Hans Koehler ◽  
Peter Schreier
Keyword(s):  
Quantitative Analysis ◽  
Stable Isotope ◽  
Isotope Dilution ◽  
Internal Standard ◽  
Stable Isotope Dilution Assay ◽  
Isotope Dilution Analysis ◽  
Model Experiments ◽  
Stable Isotope Dilution ◽  
Isotope Dilution Assay ◽  
Dilution Assay

Abstract Isotope dilution analysis was used to quantitate 2- aminoacetophenone in wines exhibiting the so- called untypical aging off-flavor. d3-Aminoacetophe- none was synthesized and used as isotopomeric internal standard. The method of quantitation was verified by several model experiments. In the off-flavored wines studied, amounts of 2-aminoacetophe none ranging from 0.7 to 12.8 μg/L were determined.

scholarly journals Quantification of Serum and Urinary S-Adenosylmethionine and S-Adenosylhomocysteine by Stable-Isotope-Dilution Liquid Chromatography-Mass Spectrometry

2004 ◽  
Vol 50 (2) ◽  
pp. 365-372 ◽  
Author(s):  
Sally P Stabler ◽  
Robert H Allen
Keyword(s):  
Mass Spectrometry ◽  
Liquid Chromatography ◽  
Stable Isotope ◽  
Isotope Dilution ◽  
Biological Fluids ◽  
Internal Standard ◽  
Fractional Excretion ◽  
Liquid Chromatography Mass Spectrometry ◽  
Stable Isotope Dilution ◽  
Chromatography Mass Spectrometry

Abstract Background: We have developed an assay that uses stable-isotope-dilution liquid chromatography–mass spectrometry to assess S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) in body fluids to investigate the relationship of these metabolites to hyperhomocysteinemia. Methods: Commercially obtained SAM (D3 methyl) and 13C5-SAH uniformly labeled in the adenosyl moiety, which was synthesized using S-adenosylhomocysteine hydrolase, were added to samples followed by perchloric acid protein precipitation, C18 chromatography, and analysis by liquid chromatography–mass spectrometry with quantification by comparison of the areas of internal standard and endogenous peaks. Results: Estimates of intraassay imprecision (CV) were 5% and 17% for SAM and SAH, respectively (n = 10). SAM decreased and SAH increased in serum and plasma samples at both 4 °C and room temperature over 80 h. SAM and SAH were unstable in samples stored longer than 2 years at −20 °C. In 48 volunteers, the estimated reference intervals [from mean (2 SD) of log-transformed data] for serum SAM and SAH were 71–168 and 8–26 nmol/L, respectively. Fractional excretion of SAM was higher than that of SAH, and the urinary SAM:SAH ratio was much higher than the serum or erythrocyte SAM:SAH ratios. Conclusions: Stable-isotope-dilution liquid chromatography–mass spectrometry can be used to quantify SAM and SAH in biological fluids and tissues. Sample handling and storage must be stringently controlled for any epidemiologic or clinical use of such assays.

Biosynthesis of 15N-labeled cylindrospermopsin and its application as internal standard in stable isotope dilution analysis

2014 ◽  
Vol 406 (24) ◽  
pp. 5765-5774 ◽  
Author(s):  
Katrin Kittler ◽  
Holger Hoffmann ◽  
Franziska Lindemann ◽  
Matthias Koch ◽  
Sascha Rohn ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Isotope Dilution ◽  
Internal Standard ◽  
Isotope Dilution Analysis ◽  
Stable Isotope Dilution Analysis ◽  
Stable Isotope Dilution

scholarly journals Quantification of α-Thujone and Its Metabolites in Human Urine after Consumption of a Sage Infusion Using Stable Isotope Dilution Assays

Toxins ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 511 ◽  
Author(s):  
Irene Thamm ◽  
Konrad Tiefenbacher ◽  
Michael Rychlik
Keyword(s):  
Detection Limit ◽  
Stable Isotope ◽  
Isotope Dilution ◽  
Human Urine ◽  
Maximum Concentration ◽  
Solid Phase Microextraction ◽  
Solid Phase ◽  
Internal Standard ◽  
Stable Isotope Dilution ◽  
Stable Isotope Dilution Assays

The metabolism of the monoterpene α-thujone was investigated in humans after consumption of sage tea, by analyses of its metabolites 2-hydroxythujone, 4-hydroxythujone, and 7-hydroxythujone in urine. For the quantitation of α-thujone and its metabolites, stable isotope dilution assays were developed. Using d6-α-thujone as internal standard, we quantified α-thujone by solid phase microextraction GC-MS and the hydroxythujones with d6-2-hydroxythujone, d6-4-hydroxythujone, and d6-7-hydroxythujone after glucuronide/sulfate deconjugation by LC-MS/MS in urine. After the consumption of 575.0 µg α-thujone, the 4-hydroxythujone and 7-hydroxythujone were detectable in the urine of the volunteers under study, after liberation from their glucuronides/sulfates. The 2-Hydroxythujone was not present in any of the volunteer samples above its detection limit. α-Thujone was detectable in a low amount, with a maximum concentration of 94 ng/L for the volunteer with the highest dose of 14.3 µg/kg bw.

Preparation of 13C-labelled cis-zearalenone and its application as internal standard in stable isotope dilution analysis

2014 ◽  
Vol 7 (1) ◽  
pp. 45-52 ◽  
Author(s):  
S. Drzymala ◽  
J. Riedel ◽  
R. Köppen ◽  
L.-A. Garbe ◽  
M. Koch
Keyword(s):  
Stable Isotope ◽  
Isotope Dilution ◽  
Edible Oils ◽  
Uv Light ◽  
Internal Standard ◽  
Edible Oil ◽  
Isotope Dilution Analysis ◽  
Stable Isotope Dilution Analysis ◽  
Stable Isotope Dilution ◽  
Maize Germ

Pure U-[13C18]-labelled cis-zearalenone (cis-ZEA) has been prepared and characterised as internal standard (ISTD) for a reliable quantification of cis-ZEA in contaminated food and feed products. The cis-isomer of the naturally trans-configurated Fusarium mycotoxin zearalenone is often neglected. However, isomerisation easily occurs by exposure of ZEA to (UV-)light. Thus, the applicability of the new cis-ZEA ISTD was demonstrated in a long-term isomerisation study comparing naturally trans-ZEA-contaminated edible oil with spiked edible oil. To estimate the benefits of the newly prepared cis-ZEA ISTD, various approaches to quantify cis-ZEA by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) were compared. As a result, a significant bias was revealed if no appropriate cis-ZEA standards are used. Furthermore, the new ISTD was applied to the analysis of 15 edible oils by stable isotope dilution analysis in combination with HPLC-electrospray ionisation-MS/MS. One of the maize germ oils showed the presence of cis-ZEA above LOD (≯0.3 μg/kg), whereas two out of 15 maize germ oils were found to be contaminated with trans-ZEA (range 17.0-31.0 μg/kg).

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