degradation of phenoxyethanol occurs in a B12-dependent manner (Frings and Schink 1994), and a recent investigation suggests that a reaction similar to that seen in Ado-B12dependent diol dehydratase is involved in the process; however no corrinoid compound has been identified thus far (Speranza 2000). Methylmalonyl-CoA mutase

      Methylmalonyl-CoA mutase (MCM) catalyzes the interconversion of (R)methylmalonyl-CoA and succinyl-CoA, and is the only carbon skeleton rearrangement that is shared in bacteria and higher animals (Flavin and Ochoa 1957, Overath et al. 1962, Allen et al. 1963, Kellermeyer et al. 1964, Fenton et al. 1982). In higher animals, this enzyme is required for the degradation of odd-chain-length fatty acids and certain branched-chain amino acids. Deficiencies in this enzyme, or those required for transport and conversion of B12-precursors to Ado-B12, lead to methylmalonic acidemia in humans (Ledley 1990, Allen et al. 1993, Qureshi et al. 1994). This disease is characterized by neuropsychiatric symptoms and if left untreated is often fatal during infancy. In some bacteria, MCM is involved in the fermentation of succinate to propionate, and in Streptomyces cinnamonensis it may be involved in the synthesis of polyketide antibiotics (Birch et al. 1993).

  S. enterica as a Model Organism for the Study of B12 Physiology and Metabolism

      To improve our understanding of B12 metabolism, Salmonella enterica has been used as a model organism to conduct molecular genetic investigations. S. enterica provides an ideal system to study many aspects of B12 physiology and metabolism: transport, biosynthesis, and its use as a cofactor in intramolecular rearrangements and methyl transfer can all be studied in this one organism. In addition, S. enterica is amenable to genetic manipulation and many methods are already in place including P22