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. 1988 Nov;170(11):5197–5199. doi: 10.1128/jb.170.11.5197-5199.1988

Enhanced acetohydroxy acid synthase III activity in an ilvH mutant of Escherichia coli K-12.

E Ricca 1, D Limauro 1, C T Lago 1, M de Felice 1
PMCID: PMC211590  PMID: 3053650

Abstract

The acetohydroxy acid synthase III isozyme, which catalyzes the first common step in the biosynthesis of isoleucine, leucine, and valine in Escherichia coli K-12, is composed of two subunits, the ilvI and ilvH gene products. A missense mutation in ilvH (ilvH612), which reduced the sensitivity of the enzyme to the end product inhibition by valine, also increased its specific activity and lowered the Km for alpha-acetolactate synthesis. The mutation increased the sensitivity of acetohydroxy acid synthase III to dialysis and heat treatment and reduced the requirement for thiamine pyrophosphate addition to the assay mixture for activity. A strain carrying the ilvH612 mutation grew better than a homologous ilvH+ strain in the presence of leucine. The data indicate that this is a consequence of a more active acetohydroxy acid synthase III isozyme rather than the result of an alteration of the leucine-mediated repression of the ilvIH operon.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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