Direct Hydrogen Transfer by Methylmalonyl Coenzyme a Mutase.

In this scheme, the racemase involves a rearrangement of the hydrogen about the asymmetrical carbon (6,7), while the mutase reaction involves an intramolecular migration (8, 9) of the thioester group (l&12). Two approaches are available to determine the source of the hydrogen that arises on carbon 3 of succinyl-CoA as a result of methylmalonyl-Coil mutase action. The first or indirect approach, namely, the use of tritiated water, has determined that this hydrogen does not originate from water (13). This approach is indicative, but not conclusive, when dilute isotopes are used, because of the possibility of isotope discrimination. Proof as to the origin of the