Interrelationships Between the Enzymes of Ethanolamine Metabolism in Escherichia coli

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Abstract
The activities of the enzymes ethanolamine ammonia-lyase, CoA-dependent and CoA-independent aldehyde dehydrogenases and isocitrate lyase were assayed in E. coli grown on various sources of C and N. Induction of ethanolamine ammonia-lyase and of maximal levels of both aldehyde dehydrogenases required the concerted effects of ethanolamine and vitamin (or coenzyme) B12. Molecular exclusion chromatography revealed that, in the absence of 1 or both co-inducers, 2 repressible isoenzymes of Co-A-dependent aldehyde dehydrogenase (MW 900,000 and 120,000) were produced, these being replaced by 2 inducible isoenzymes (MW 520,000 and 370,000) in the presence of both co-inducers. A similar inducible repressible series of isoenzymes was also observed for CoA-independent aldehyde dehydrogenase. No evidence was found for structural relationships between ethanolamine ammonia-lyase, CoA-dependent aldehyde dehydrogenase and CoA-independent aldehyde dehydrogenase, but mutant and physiological studies demonstrated that the induction of the 1st 2 enzymes is under common control. Evidence is presented for the operation of a previously unreported pathway of ethanolamine metabolism in E. coli.

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