Compartmentation in the induction of the hexose-6-phosphate transport system of Escherichia coli

Abstract

The induction of the hexose-6-phosphate transport system was investigated. Glucose-6-phosphate (G6P) at concentrations as low as 10(-4)m was able to induce this system in wild-type cells, as well as in mutants lacking phosphoglucose isomerase or G6P dehydrogenase. Growth in the presence of fructose-6-phosphate (F6P) induced the system only if the cells contained phosphoglucose isomerase. Furthermore, glucose and F6P were found to induce the system only if the extracellular concentration of G6P became appreciable in the medium as a consequence of the leakage of intracellular G6P formed from the glucose or F6P. Intracellular G6P was not an inducer even at high concentrations. The metabolism of glucose inhibited the induction of the hexose-6-phosphate transport system. Hypotheses for this compartmentalization of inducer and membrane-associated induction are presented.