Inhibition of acetohydroxy acid synthase by leucine

Natan Gollop, David M. Chipman, Ze'ev Barak

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


The enzymatic reaction of acetohydroxy acid synthase in crude extracts of Escherichia coli K-12 is inhibited by leucine. Inhibition is most pronounced at low pH values and is low at pH values higher than 8.0. Both isoenzymes of acetohydroxy acid synthase present in E. coli K-12 (isoenzyme I and isoenzyme III) are inhibited by leucine. Isoenzyme I, which is responsible for the majority of acetohydroxy acid synthase activity in E. coli K-12 at physiological pH, is inhibited almost completely by 30 mM leucine at pH 6.25-7.0 and is not affected at all at pH values higher than 8.4. Inhibition of isoenzyme I by leucine is a mixed noncompetitive process. Leucine inhibition of isoenzyme III is pH-independent and reaches only 40% at 30 mM leucine. The inhibition of acetohydroxy acid synthase by leucine at physiological pH, observed in vitro in this study, correlates with the idea that acetohydroxy acid synthase is a target for the toxicity of the abnormally high concentrations of leucine in E. coli K-12.

Original languageEnglish
Pages (from-to)34-39
Number of pages6
JournalBiochimica et Biophysica Acta - Proteins and Proteomics
Issue number1
StatePublished - 17 Oct 1983


  • (E. coli)
  • Acetohydroxy acid synthase
  • Leucine inhibition

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology


Dive into the research topics of 'Inhibition of acetohydroxy acid synthase by leucine'. Together they form a unique fingerprint.

Cite this