The Phosphoenolpyruvate-initiated Pathway of Fructose Metabolism in Escherichia cloZi*

The inability of a particular Escherichiu coZi mutant to form colonies on fructose minimal medium is ascribed to the inhibition of growth by glucose 6-phosphate, which accumulates in this strain from a small amount of glucose in the fructose. This explanation requires that fructose metabolism not be initiated by its phosphorylation to fructose 6-phosphate. Experiments in vitro show that fructose is phosphorylated to fructose l-phosphate in a reaction catalyzed by the phosphoenolpyruvate phosphotransferase system. Fructose l-phosphate is converted to fructose 1,6-diphosphate by an inducible kinase, as has been found in other organisms. Thus, fructose should be considered a gluconeogenic carbon source in E. coli.