@article{mbs:/content/journal/micro/10.1099/00221287-127-1-19, author = "Squires, Charles H. and Levinthal, Mark and De Felice, Maurilio", title = "A Role for Threonine Deaminase in the Regulation of α-Acetolactate Biosynthesis in Escherichia coli K12", journal= "Microbiology", year = "1981", volume = "127", number = "1", pages = "19-25", doi = "https://doi.org/10.1099/00221287-127-1-19", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-127-1-19", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", abstract = "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.", }