Dioldehydrase, reaction

Frey, P. A., Essenberg, M. K., and Abeles, R. H., 1967, Studies on the mechanism of hydrogen transfer in the cobamide coenzyme-dependent dioldehydrase reaction. J. Biol. Chem. 242 5369n5377. 

Based on isotope exchange experiments with dioldehydrase. Abeles (103) postulated the following general mechanism for the hydrogen transfer reaction. 

The enzymatic reactions in which adenosylcobalamin was known to serve as coenzyme by 1964 were those of glutamate mutase, methylmalonyl-CoA mutase (MCM), " propane-1,2-diol hydro-lyase (dioldehydrase, DDH), and glycerol hydro-lyase (glycerol dehydrase), shown in Equations (1)—(4). 

The B12 coenzymes act in concert with a number of enzymes, but it has so far proved difficult to elucidate their role in detail. Perhaps the best studied systems25 involve the dioldehydrases, where the following reactions are... 

Dioldehydrase, in the presence of vitamin B12 coenzyme, catalyzes the conversion ofvor -propanediol and ethyl-eneglycol to propionaldehyde and acetaldehyde. Substrate C-1 tritium replaces the tux) C-5 hydrogens of the coenzyme and occupies the a position of the product aldehyde. When Bi2 coenzyme containing C-5 tritium is used with noniso-topic substrates, tritium is transferred to the a position of the product. The rate of these reactions is consistent with a mechanism in which the coenzyme functions as intermediate hydrogen carrier. 

Table I is a summary of all of the reactions known to date which require vitamin B12 coenzyme (i). The reaction catalyzed by glutamate mutase, the first reaction in which vitamin B12 was known to be involved, was discovered by Barker and his coworkers. The second reaction is the only one of these which also occurs in mammals all other reactions occur in bacteria. Much of the experimental data described here will be derived from the enzyme called dioldehydrase. An additional reaction which is not shown is the conversion of nucleotides to deoxynucleotides. The conversion of —CHOH— to — CH2— is in some way very similar to the reaction catalyzed by dioldehydrase. Vitamin B12 coenzyme-depend-...

For example, methylmalonyl-CoA mutase catalyzes a reaction in which the H bonded to one carbon changes places with an C(=0)SCoA group bonded to an adjacent carbon. In the reaction catalyzed by dioldehydrase, an H and an OH change places. (A mutase is an enzyme that transfers a group from one position to another.)... 

T. Toraya, E. Krodel, A. S. Mildran, and R. H. Abeles (1979), Role of peripheral side chains of vitamin 6 2 coenzymes in the reaction catalyzed by dioldehydrase. Biochemistry 18, 417-426. 

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