Evaluation of isotope discrimination in 13C-based metabolic flux analysis

In a C-13 experiment for metabolic flux analysis (C-13 MFA), we examined isotope discrimination by measuring the labeling of glucose, amino acids, and hexose monophosphates via mass spectrometry. When Escherichia coli grew in a mix of 20% fully labeled and 80% naturally labeled glucose medium, the cell metabolism favored light isotopes and the measured isotopic ratios (delta C-13) were in the range of -35 to -92. Glucose transporters might play an important role in such isotopic fractionation. Flux analysis showed that both isotopic discrimination and isotopic impurities in labeled substrates could affect the solution of C-13 MFA. (C) 2011 Elsevier Inc. All rights reserved.