Utilization of fructose and fructose 1-phosphate by Escherichia coli.

1. The phosphoenolpyruvate (PEP): fructose phosphotransferase system plays a key role in the utilization of fructose by Escherichia coli. Mutants devoid of, or altered in, this system are not only modified in their ability to phosphorylate fructose but are also altered in their ability to take up this hexose from solutions. 2. The major product of fructose phosphorylation in E. coli is fructose 1-phosphate, though fructose 6-phosphate can also be formed by a PEP-dependent mechanism. The relationship between PEP: fructose 1- and PEP: fructose 6-phosphotransferase activities is discussed. 3. PEP-dependent fructose phosphorylation, fructose uptake by whole cells and ATP-dependent fructose 1-phosphate phosphorylation to fructose 1, 6-diphosphate are activities that, in E. coli, are induced by fructose. A regulatory mutant that exhibits these activities constitutively has been isolated; its properties indicate that the expression of fructose-induced proteins is controlled as a regulon. 4. The utilization of fructose by E. coli is subject to control at the level of fructose entry into whole cells. Fructose uptake is inhibited by intracellular hexose phosphates or by carbon sources that can readily give rise to hexose phosphates, such as glucose or galactose. 5. Fructose 1-phosphate can serve as a sole carbon source for the growth of E. coli. Fructose 1-phosphate, like other hexose-phosphates such as glucose 6-phosphate and fructose 6-phosphate, is a substrate of an inducible hexose phosphate transport system. However, unlike glucose 6-phosphate, fructose 1-phosphate, when present in the growth medium of E. coli, does not give rise to the induction of this uptake system.