Cadmium Reactivity in Metal-Contaminated Soils Using a Coupled Stable Isotope Dilution−Sequential Extraction Procedure

2001 ◽  
Vol 35 (1) ◽  
pp. 121-126 ◽  
Author(s):  
Zoe Ann S. Ahnstrom ◽  
David R. Parker
Keyword(s):  
Stable Isotope ◽  
Sequential Extraction ◽  
Isotope Dilution ◽  
Contaminated Soils ◽  
Extraction Procedure ◽  
Sequential Extraction Procedure ◽  
Stable Isotope Dilution

scholarly journals Development of a Stable-Isotope Dilution Assay for γ-Aminobutyric Acid (GABA) Transaminase in Isolated Leukocytes and Evidence That GABA and β-Alanine Transaminases Are Identical

2001 ◽  
Vol 47 (3) ◽  
pp. 525-531 ◽  
Author(s):  
Danielle S M Schor ◽  
Eduard A Struys ◽  
Boris M Hogema ◽  
K Michael Gibson ◽  
Cornelis Jakobs
Keyword(s):  
Enzyme Activity ◽  
Stable Isotope ◽  
Glutamic Acid ◽  
Isotope Dilution ◽  
Solid Phase ◽  
Extraction Procedure ◽  
Internal Standard ◽  
Aminobutyric Acid ◽  
Dilution Method ◽  
Stable Isotope Dilution

Abstract Background: Several methods have been published for measuring γ-aminobutyric acid transaminase (GABA-T) activity, but these methods are either impracticable because of the use of radioisotopes or insufficiently sensitive to determine small enzyme activities in leukocyte extracts. We developed a direct and sensitive enzyme method. Methods: We developed a stable-isotope dilution method for the measurement of [15N]glutamic acid derived from [15N]GABA and α-ketoglutaric acid, catalyzed by GABA-T. The method for analysis of [15N]glutamic acid comprised a solid-phase extraction procedure to isolate this analyte from incubation samples. After derivatization, [15N]glutamic acid was quantified by gas chromatography–mass spectrometry relative to its 2H5-labeled internal standard. In addition to [15N]GABA, [15N]β-alanine was a cosubstrate. Results: GABA-T-deficient lymphoblasts showed diminished enzyme activity, with both [15N]GABA and [15N]β-alanine as substrate. Vigabatrin inhibited the enzyme activity for both substrates. Conclusions: The activity of GABA-T can be accurately determined by our procedure using 15N-labeled substrate, measuring the formation of [15N]glutamic acid. Our results with [15N]β-alanine indicate that GABA and β-alanine transaminases are identical.

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