title: Mechanism of action of adenosylcobalamin: hydrogen transfer in the inactivation of diol dehydratase by glycerol.
abstract: We have investigated the kinetic characteristics of the inactivation of the adenosylcobalamin-dependent enzyme propanediol dehydratase 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 hydrogen (or deuterium) 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 hydrogen carrier, presumably in the form of 5'-deoxyadenosine. Moreover, a mechanism involving a rate-determining transfer of hydrogen from an intermediate containing three equivalent hydrogens quantitatively accounts for all of the results. When diol dehydratase holoenzyme is inactivated by [1-3H]glycerol, 5'-deoxyadenosine which is enriched in tritium by a factor of 2.1 over that in glycerol can be isolated from the reaction mixture.
mesh_terms: D003038:Cobamides; D003903:Deuterium; D005990:Glycerol / Q000494:pharmacology*; D006836:Hydro-Lyases / Q000037:antagonists & inhibitors*; D007553:Isotope Labeling; D007700:Kinetics; D008433:Mathematics; D011408:Propanediol Dehydratase / Q000037:antagonists & inhibitors*
chemical_list: D003038:Cobamides; D003903:Deuterium; D006836:Hydro-Lyases; D011408:Propanediol Dehydratase; C000913:cobamamide; D005990:Glycerol