Mechanism of action of adenosylcobalamin: hydrogen transfer in the inactivation of diol dehydratase by glycerol

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Abstract
The kinetic characteristics of the inactivation of the adenosylcobalamin-dependent enzyme propranediol dehydratase [EC 4.2.1.28 from Klebsiella pneumoniae] by glycerol, (RS)-1,1-dideuterioglycerol, (R)-1,1-dideuterioglycerol and perdeuterioglycerol in the presence of 1,2-propanediol and 1,1-dideuterio-1,2-propanediol. The results imply that H (or 2H) attached to C-1 of 1,2-propanediol participates in the inactivation process and contributes to the expression of a kinetic isotope effect on the rate of inactivation. The mechanism for this inactivation must involve the cofactor as an intermediate H carrier, presumably in the form of 5''-deoxyadenosine. A mechanism involving a rate-determining transfer of H from an intermediate containing 3 equivalent H quantitatively accounts for all of the results. When diol dehydratase holoenzyme is inactivated by [1-3H]glycerol, 5''-deoxyadenosine which is enriched in 3H by a factor of 2.1 over that in glycerol can be isolated from the reaction mixture.

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