f A Role for Threonine Deaminase in the Regulation of α-Acetolactate Biosynthesis in Escherichia coli K12
- Authors: CHARLES H. SQUIRES†, MARK LEVINTHAL, MAURILIO DE FELICE
- First Published Online: 01 November 1981, Microbiology 127: 19-25, doi: 10.1099/00221287-127-1-19
- Subject: Physiology And Growth
- Issue Published:
The flow of carbon to α-acetolactate in Escherichia coli K12 is shown to involve the endogenous pool of α-ketobutyrate (α-KB). In vivo, the acetohydroxy acid synthase (AHAS) isoenzymes have an affinity for α-KB sufficiently high that α-acetolactate production is severely limited when α-KB is supplied exogenously. The ability of threonine deaminase to make α-KB is correlated with the synthesis of the AHAS isoenzymes. Mutations in ilvA that alter the catalytic and allosteric properties of threonine deaminase affect α-KB production and the expression of the AHAS isoenzymes in a direct way. The ilvA538 mutation results in a feedback-hypersensitive threonine deaminase and slow α-KB and AHAS production. A spontaneous revertant of an ilvA538 strain expressing a feedback-resistant threonine deaminase produces α-KB and AHAS more quickly. A physiological role for the activator (valine) site on threonine deaminase is proposed and valine is shown to increase α-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 α-KB in the biosynthesis of acetolactate are discussed.
Present address: Synergen, 1885 33rd Street, Boulder, Colorado 80301, U.S.A.
© Society for General Microbiology, 1981 | Published by the Microbiology Society
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