<p>Mannitol dehydrogenases catalyse the NAD-dependent reduction of mannitol-1-phosphates as part of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The PTS facilitates the vectorial translocation of metabolisable carbohydrates to form the corresponding sugar phosphates, which are then converted to glycolytic intermediates [<cite idref="PUB00002028"/>]. Mannitol 2-dehydrogenase catalyses the NAD-dependent reduction of mannitol to fructose [<cite idref="PUB00003120"/>].Several dehydrogenases have been shown [<cite idref="PUB00003120"/>] to be evolutionary related, including mannitol-1-phosphate 5-dehydrogenase (<db_xref db="EC" dbkey="1.1.1.17"/>) (gene mtlD), mannitol 2-dehydrogenase (<db_xref db="EC" dbkey="1.1.1.67"/>) (gene mtlK); mannonate oxidoreductase (<db_xref db="EC" dbkey="1.1.1.57"/>) (fructuronate reductase) (gene uxuB); <taxon tax_id="562">Escherichia coli</taxon> hypothetical proteins ydfI and yeiQ; and yeast hypothetical protein YEL070w.</p>