title: A role for threonine deaminase in the regulation of alpha-acetolactate biosynthesis in Escherichia coli K12.
abstract: The flow of carbon to alpha-acetolactate is Escherichia coli K12 is shown to involve the endogenous pool of alpha-ketobutyrate (alpha-KB). In vivo, the acetohydroxy acid synthase (AHAS) isoenzymes have an affinity for alpha-KB sufficiently high that alpha-acetolactate production is severely limited when alpha K-B is supplied exogenously. The ability of threonine deaminase to make alpha-KB is correlated with the synthesis of the AHAS isoenzymes. Mutations in ilvA that alter the catalytic and allosteric properties of threonine deaminase affect alpha-KB production and the expression of the AHAS isoenzymes in a direct way. The ilv A538 mutation results in a feedback-hypersensitive threonine deaminase ans slow alpha-KB and AHAS production. A spontaneous revertant of an ilvA538 strain expressing a feedback-resistant threonine deaminase produces alpha-KB and AHAS more quickly. A physiological role for the activator (valine) site on threonine deaminase is proposed and valine is shown to increase alpha-KB production in vivo. Valine can thus regulate its own biosynthetic pathway without jeopardizing the production of isoleucine. The physiological implications of the role of alpha-KB in the biosynthesis of acetolactate are discussed.
mesh_terms: D000095:Acetolactate Synthase / Q000096:biosynthesis; D002087:Butyrates / Q000096:biosynthesis / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D007773:Lactates / Q000096:biosynthesis*; D009154:Mutation; D013913:Threonine Dehydratase / Q000502:physiology*; D014633:Valine / Q000096:biosynthesis / Q000494:pharmacology
chemical_list: D002087:Butyrates; D007773:Lactates; C006359:alpha-acetolactate; C005087:alpha-ketobutyric acid; D000095:Acetolactate Synthase; D013913:Threonine Dehydratase; D014633:Valine