The anaerobic fermentation of glucose by Leuconostoc mesenteroides via the reductive pentose phosphate pathway leads to the accumulation of lactic acid and ethanol. The isotope redistribution coefficients (a ij ) that characterize the specific derivation of each hydrogen atom in ethanol in relation to the non-exchangeable hydrogen atoms in glucose and the medium water have been determined using quantitative 2 H NMR. First, it is confirmed that the hydrogens of the methylene group are related only to the 1 and 3 positions of glucose via the NAD(P)H pool and not to the 4 position, in contrast to ethanol produced by Saccharomyces cerevisiae. Second, it is found that the conversion factors (C f ) for the transfer of hydrogen to the pro-S and pro-R positions of the methylene group are not equivalent: the C f -1-R:C f -1-S ratio is 2.1, whereas the C f -3-R:C f -3-S ratio is 0.8. It is shown that this non-equivalence is not determined by the stereochemistry of the terminal NADH-and NADPH-dependent alcohol dehydrogenases, but is dependent on the cofactor selectivities of the reductive and oxidative steps of the reduced nucleotide cycle.

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