Acetohydroxyacid synthase isozyme I from Escherichia coli has unique catalytic and regulatory properties

Valerie Vinogradov, Maria Vyazmensky, Stanislav Engel, Inna Belenky, Alexander Kaplun, Olga Kryukov, Ze'ev Barak, David M. Chipman

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


AHAS I is an isozyme of acetohydroxyacid synthase which is apparently unique to enterobacteria. It has been known for over 20 years that it has many properties which are quite different from those of the other two enterobacterial AHASs isozymes, as well as from those of "typical" AHASs which are single enzymes in a given organism. These include a unique mechanism for regulation of expression and the absence of a preference for forming acetohydroxybutyrate. We have cloned the two subunits, ilvB and ilvN, of this Escherichia coli isoenzyme and examined the enzymatic properties of the purified holoenzyme and the enzyme reconstituted from purified subunits. Unlike other AHASs, AHAS I demonstrates cooperative feedback inhibition by valine, and the kinetics fit closely to an exclusive binding model. The formation of acetolactate by AHAS I is readily reversible and acetolactate can act as substrate for alternative AHAS I-catalyzed reactions.

Original languageEnglish
Pages (from-to)356-363
Number of pages8
JournalBiochimica et Biophysica Acta - General Subjects
Issue number3
StatePublished - 1 Mar 2006


  • Allosteric
  • Isozyme
  • Oxygenase
  • Peracetate
  • R-PAC
  • Valine inhibition

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology


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