EC - Acetolactate synthase

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IntEnz Enzyme Nomenclature


Accepted name:
acetolactate synthase
Other names:
α-acetohydroxy acid synthetase
α-acetohydroxyacid synthase
α-acetolactate synthase
α-acetolactate synthetase
acetohydroxy acid synthetase
acetohydroxyacid synthase
acetolactate pyruvate-lyase (carboxylating)
acetolactic synthetase
Systematic name:
pyruvate:pyruvate acetaldehydetransferase (decarboxylating)




This enzyme requires thiamine diphosphate. The reaction shown is in the pathway of biosynthesis of valine; the enzyme can also transfer the acetaldehyde from pyruvate to 2-oxobutanoate, forming 2-ethyl-2-hydroxy-3-oxobutanoate, also known as 2-aceto-2-hydroxybutanoate, a reaction in the biosynthesis of isoleucine.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Protein domains and families: PROSITE:PDOC00166
Structural data: CSA , EC2PDB
Gene Ontology: GO:0003984
CAS Registry Number: 9027-45-6
UniProtKB/Swiss-Prot: (79) [show] [UniProt]


  1. Bauerle, R.H., Freundlich, M., Størmer, F.C. and Umbarger, H.E.
    Control of isoleucine, valine and leucine biosynthesis. II. Endproduct inhibition by valine of acetohydroxy acid synthetase in Salmonella typhimurium.
    Biochim. Biophys. Acta 92 : 142-149 (1964).
  2. Huseby, N.E., Christensen, T.B., Olsen, B.R. and Størmer, F.C.
    The pH 6 acetolactate-forming enzyme from Aerobacter aerogenes. Subunit structure.
    Eur. J. Biochem. 20 : 209-214 (1971). [PMID: 5560406]
  3. Størmer, F.C., Solberg, Y. and Hovig, T.
    The pH 6 acetolactate-forming enzyme from Aerobacter aerogenes. Molecular properties.
    Eur. J. Biochem. 10 : 251-260 (1969). [PMID: 5823101]
  4. Barak, Z., Chipman, D.M. and Gollop, N.
    Physiological implications of the specificity of acetohydroxy acid synthase isozymes of enteric bacteria.
    J. Bacteriol. 169 : 3750-3756 (1987). [PMID: 3301814]
  5. Pang, S. S., Duggleby, R. G., Schowen, R. L., Guddat, L. W.
    The crystal structures of Klebsiella pneumoniae acetolactate synthase with enzyme-bound cofactor and with an unusual intermediate.
    J. Biol. Chem. 279 : 2242-2253 (2004). [PMID: 14557277]

[EC created 1972 as EC, transferred 2002 to EC]