title: Intermolecular tritium transfer in the transcarboxylase reaction.
abstract: Transfer of tritium from [3-3H]pyruvate into propionyl-CoA is found during the reaction of transcarboxylase: Methylmalonyl-CoA + pyruvate leads to oxalacetate + propionyl-CoA. About 5% of the tritium counts that are labilized in the reaction are found in a position of the propionate that exchanges rapidly with water in the presence of transcarboxylase. Transfer from [2-3H]propionate of propionyl-CoA to pyruvate is real but only about one-tenth as great. The tritium transfers between reactants on two subunits are difficult to explain by a "carbanion" mechanism of --C--H bond cleavage and support the cyclic mechanism in which carboxybiotin itself is the base and the enol form of biotin is the proton-transferring agent.
mesh_terms: D019878:Carboxyl and Carbamoyl Transferases; D003065:Coenzyme A / Q000378:metabolism; D011422:Propionates / Q000378:metabolism; D011424:Propionibacterium / Q000201:enzymology; D011773:Pyruvates / Q000378:metabolism; D014166:Transferases / Q000378:metabolism*; D014316:Tritium
chemical_list: D011422:Propionates; D011773:Pyruvates; D014316:Tritium; D014166:Transferases; D019878:Carboxyl and Carbamoyl Transferases; C021580:Methylmalonyl-CoA carboxytransferase; D003065:Coenzyme A