14 Coenzyme Bl2-Dependent Mutases Causing Carbon Chain Rearrangements

Publisher Summary This chapter discusses the coenzyme B 12 -dependent mutases causing carbon chain rearrangements. Three B 12 coenzyme-dependent enzymes catalyzing carbon skeleton rearrangements are known: glutamate mutase, methylmalonyl-CoA mutase, and methyleneglutarate mutase. The reactions catalyzed by these enzymes are similar in that they all involve rearrangements in which a substituent group is moved between the α and β positions of a propionate residue, while a hydrogen atom is moved in the opposite direction. The glutamate mutase reaction was discovered during the studies of the path of glutamate fermentation by Clostridium tetanomorphum . The extracts of this bacterium were found to convert glutamate reversibly to ammonia and mesaconate (2-methylfumaric acid)—a carbon, branched chain compound. In the synthesis of propionate by propionibacteria, the mutase reaction functions in the reverse direction from succinyl-CoA to ( R )-methyl-malonyl CoA. A methylmalonyl-CoA racemase is also required in propionate synthesis to form ( S )-methylmalonyl-CoA, which then reacts with pyruvate in a transcarboxylation reaction to give propionyl-CoA and oxalacetate.