Ethanolamine ammonia lyase

     Ado-B12-dependent ethanolamine ammonia lyase is used for ethanolamine

degradation (Bradbeer 1965, Scarlett and Turner 1976). The pathway for ethanolamine degradation is analogous to that for PD: ethanolamine is converted to acetaldehyde with the concomitant loss of ammonia and is further metabolized to both ethanol and acetic acid. This process in addition to providing an energy and carbon source, also provides a source of nitrogen. The induction of the eut operon requires both ethanolamine and B12, and unlike PD ethanolamine does not induce the de novo synthesis of B12 (Rondon and Escalante-Semerena 1992, Chen et al. 1995, Bobik et al. 1997) Ethanolamine is encountered frequently in nature as a component of the lipids, phosphatidyl ethanolamine and phosphatidyl choline.

Glycerol dehydratase

     This enzyme converts glycerol to 3-hydroxypropionaldehyde, which can

subsequently be reduced to 1,3-propanediol, a commercially important compound used in the manufacturing of carpet backing (Homann et al. 1990, Witt et al. 1994). This reaction provides a means to regenerate reducing equivalents produced by glycerol dehydrogenase. Glycerol is commonly found as the backbone of lipids. Methionine synthetase

     The final step in the synthesis of methionine in both humans and many bacteria requires CH3-B12-dependent methionine synthetase, an enzyme that serves to transfer methyl groups from methyltetrahydrofolate to homocysteine. Methionine synthase is one of the better studied B12-dependent enzymes partly because defects in this enzyme result in hyperhomocysteinuria, a possible risk factor in heart disease (Refsum et al. 1998, Siri et al. 1998). Both Salmonella spp. and E. coli present ideal models to study this enzyme