Savidge, W. B. North Carolina State University, email@example.com
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THE INTRAMOLECULAR ISOTOPIC COMPOSITION OF GLUTAMATE AS AN INDICATOR OF AMINO ACID METABOLISM IN AUTOTROPHS AND HETEROTROPHS
Amino acids are assembled via two primary pathways. Different isotopic fractionations associated with these two pathways lead to intramolecular isotopic heterogeneities within some amino acids. The magnitude of the intramolecular isotopic differences within these amino acids can be used to investigate aspects of the amino acid metabolism in plants and animals.
The carbon isotopic composition of the carboxyl carbon (C1) of glutamate and the total hydrolyzable carbon fraction from a variety of autotrophs and heterotrophs were compared to ascertain what factors influenced the isotopic heterogeneity expressed within the molecule. Among autotrophs, the isotopic heterogeneity within the glutamate molecule was a function of the secondary carboxylase present within the plant. The in vivo isotopic fractionation in PEPCK-utilizing macroalgae was estimated to be -14.5 +/- 5.2 per mil relative to the intracellular CO2 pool. The isotopic composition of glutamate in multicellular heterotrophs appears very similar to that of potential food resources. Amino acids, including non-essential amino acids such as glutamate, seem to be assimilated from the diet into animal tissues without significant isotopic modification. Cultured microbial heterotrophs display little isotopic heterogeneity within the glutamate molecule. Carboxyl carbons are derived from a respiratory CO2 pool that does not differ greatly from microbial biomass.
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