The Effect of Carbon and Nitrogen Sources on the Level of Metabolic Intermediates in Escherichia coli

Abstract

The levels of glycolytic intermediates, selected amino acids, and citric acid cycle intermediates have been measured in Escherichia coli in logarithmic growth on a variety of carbon and nitrogen sources, and also after rapid addition of nitrients to cultures. The results have been used to assess the regulatory role of various metabolites in E. coli. Gluconeogenesis is associated with high phosphoenolpyruvate levels and low levels of fructose 1,6-diphosphate, in agreement with the proposed regulatory mechanisms for phosphofructokinase, pyruvate kinase, and phosphoenolpyruvate carboxylase. Isotopic experiments indicate that considerable gluconeogenesis occurs in succinate- or glycerol-grown cells after the addition of glucose, although the levels of glycolytic intermediates resemble those of glucose-grown cells, indicating that control gluconeogenesis is leaky. The levels of adenosine triphosphate are lower in slowly growing cells, limited either by the availability of carbon (cells grown on acetate-NH4Cl) or by the availability of nitrogen (cells grown on glucose-glycine). These changes reflect primarily changes in the total adenine nucleotide pool, rather than major changes in the ratio of various adenine nucleotides. Measurements of the level of metabolic intermediates in acetate-grown cells, before and after the addition of glucose, suggest that isocitrate lyase is controlled in vivo by metabolites other than phosphoenolpyruvate, and that both isocitrate lyase and isocitrate dehydrogenase play roles in regulating isocitrate utilization.