| Popis: |
In 1984, only two B12- dependent enzymes were known in Salmonella, ethanolamine ammonia lyase, required for use of ethanolamine (EA) as a nitrogen and carbon source, and a methyltransferase involved in cysteine biosynthesis. A genetic analysis of ethanolamine utilization was undertaken in John Roth’s laboratory in part to explore whether ethanolamine degradation contributes to the selective forces that maintain the ability to synthesize B12. Identification of the enzymes encoded in the eut operon suggests that ethanolamine degradation is an integral part of a network of reactions involving both reduction and oxidation of ethanolamine as well as fixation of CO2. EA can be used aerobically as a carbon, energy, and nitrogen source in the presence of Ado-B12 or a suitable corrinoid precursor. Under anaerobic conditions, EA can be used as a carbon source when tetrathionate is provided as an electron acceptor. Induction of the 17-gene eut operon requires the EutR regulatory protein and two effectors: EA, the substrate for the degredative pathway, and Ado-B12, the effector for EutBC lyase, which catalyzes the first step in the pathway. Induction of the operon is under autogenous control by eutR, the regulatory gene positioned at the end of the operon transcript. The eutT gene encodes an adenosyltransferase that plays a role in maintaining levels of Ado-B12 sufficient for eutT operon induction and lyase activity. |
