Conversion of D-mannitol to D-ribose: a newly discovered pathway in Escherichia coli

A mutant (mtlD) strain of Escherichia coli unable to oxidize mannitol-1-phosphate to fructose-6-phosphate was used to study the fate of mannitol-1-phosphate. D-[1-14C]mannitol entered the cells via the phosphotransferase system and was phosphorylated equally at carbon 1 or 6. The label disappeared gradually from the mannitol-1-phosphate pool, and some 60% of the 14C was recovered in nucleic acids. Ribose was isolated from the purified RNA. The 14C label distribution in the isolated ribose precluded a simple hexose-to-pentose conversion by elimination of one terminal carbon from mannitol-1-phosphate. The 14C from mannitol-1-phosphate that did not enter macromolecules was found in CO2 and in some organic, non-phosphorylated compounds that were not identified. We suggest that the de novo synthesis of mannitol-1-phosphate in E. coli may be a reaction specifically dedicated to the biosynthesis of ribose.