| 15N Investigation into the Effect of a Pollutant on the Nitrogen Metabolism of Tetrahymena pyriformis as a Model for Environmental Medical Research Kerstin Arndt,1 Diana Hofmann,2 Matthias Gehre,2 and Peter Krumbiegel1 1Department of Human Exposure Research and Epidemiology and 2Department of Analytical Chemistry, UFZ Centre for Environmental Research Leipzig-Halle, Permoserstraße 15, 04318 Leipzig, Germany Abstract
A pilot study was performed to examine the potential of stable isotope techniques for monitoring the impact of a harmful substance on the cellular nitrogen metabolism in the ciliate species Tetrahymena pyriformis. After identical cultivation periods of control cells and toluene-exposed cells in a defined culture medium enriched with [guanidino-15N2]l-arginine, a number of nitrogen-containing pools were analyzed: 1) quantity and 15N abundance of ammonia as the end product of nitrogen metabolism in the system ; 2) pattern and 15N abundances of the protein-bound amino acids in the cells ; 3) pattern and 15N abundances of free amino acids in the cells ; and 4) pattern and 15N abundances of the amino acids in the culture medium. In addition to 15N emission spectrometry, a new gas chromatography/combustion interface-isotope ratio mass spectrometry/mass spectrometry analytical system was used. The production and 15N content of ammonia were higher in the toluene-exposed system by 30% and 43%, respectively, indicating higher deamination rates and greater arginine consumption. The toluene-exposed cells exhibited increased 15N abundances of protein-bound amino acids in alanine, aspartic acid, glutamic acid, and tyrosine. Furthermore, structural analyses revealed the presence of N -acetylarginine and pyrrolidonecarboxylic acid--compounds that had not previously been detected in Tetrahymena pyriformis. Differences in the 15N-enrichment of free amino acids were also evident. This new effect-monitoring system designed to investigate the impact of a pollutant on protein metabolism by using a stable isotope-labeled cell culture is a powerful tool for environmental medical research. Key words: amino acids, GC-C-IRMS, GC-MS, nitrogen 15, nitrogen metabolism, stable isotopes, Tetrahymena pyriformis, tracer technique, volatile organic compounds. Environ Health Perspect 106:493-497 (1998) . [Online 9 July 1998] http://ehpnet1.niehs.nih.gov/docs/1998/106p493-497arndt/ abstract.html Address correspondence to P. Krumbiegel, UFZ Centre for Environmental Research Leipzig-Halle, Department of Human Exposure Research and Epidemiology, Permoserstraße 15, 04318 Leipzig, Germany. Received 22 January 1998 ; accepted 7 April 1998.
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