Chirality of the Hydrogen Transfer to the Coenzyme Catalyzed by Ribitol Dehydrogenase fromKlebsiella Pneumoniaeand D-Mannitol 1-Phosphate Dehydrogenase fromEscherichia coli

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Abstract
The stereochemistry of the hydrogen transfer to NAD catalyzed by ribitol dehydrogenase (ribitol:NAD+ 2-oxidoreductase, EC 1.1.1.56) from K. pneumoniae and D-mannitol-1-phosphate dehydrogenase (D-mannitol-1-phosphate:NAD+ 2-oxidoreductase, EC 1.1.1.17) from E. coli was investigated. [4-3H]NAD was enzymatically reduced with nonlabeled ribitol in the presence of ribitol dehydrogenase and with nonlabeled D-mannitol 1-phosphate and D-mannitol 1-phosphate dehydrogenase, respectively. In both cases the [4-3H]NADH produced was isolated and the chirality at the C-4 position determined. After the transfer of hydride, the label was in both reactions exclusively confined to the (4R) position of the newly formed [4-3H]NADH. The hydrogen transferred from the nonlabeled substrates to [4-3H]NAD apparently entered the (4S) position of the nicotinamide ring. These data indicate for both investigated inducible dehydrogenases a classification as B or (S) type enzymes. Ribitol is also dehydrogenated by the constitutive A-type L-iditol dehydrogenase. (L-iditol:NAD+ 5-oxidoreductase, EC 1.1.1.14) from sheep liver. When L-iditol dehydrogenase utilizes ribitol as hydrogen donor, the same A-type classification for this oxidoreductase, as expected, holds true. For the 1st time, opposite chirality of hydrogen transfer to NAD+ in 1 organic reaction.sbd.ribitol + NAD+ = D-ribulose + NADH + H+.sbd.is observed when 2 different dehydrogenases, the inducible ribitol dehydrogenase from K. pneumoniae and the constitutive L-iditol dehydrogenase from sheep liver, are used as enzymes. This result contradicts the previous generalization that the chirality of hydrogen transfer to the coenzyme for the same reaction is independent of the source of the catalyzing enzyme.

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