Fate of the Oxygen Atoms in the Diol-Dehydratase-Catalyzed Dehydration of meso-Butane-2,3-diol

18O-Substituted propane-1,2-diols and meso-butane-1,2-diols were synthesized and fed to growing cells of Lactobacillus brevis. Propan-1-ol and butan-2-ol, prepared from such diols through diol-dehydratase-catalyzed dehydration followed by intracellular reduction, were analyzed for their 18O-content. For each propane-1,2-diol enantiomer, partial retention or complete loss of the isotope appeared to be related to the mode of substrate binding. Specific retention of the O-atom linked to the (R)-configured C-atom of meso-butane-1,2-diol indicates that the diol dehydratase handles this substrate like (R)-propane-1,2-diol.