EC - Ketol-acid reductoisomerase (NADP+)

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IntEnz Enzyme Nomenclature


Accepted name:
ketol-acid reductoisomerase (NADP+)
Other names:
2-hydroxy-3-keto acid reductoisomerase
α-keto-β-hydroxylacyl reductoisomerase
acetohydroxy acid isomeroreductase
acetohydroxy acid reductoisomerase
acetolactate reductoisomerase
dihydroxyisovalerate (isomerizing) dehydrogenase
dihydroxyisovalerate dehydrogenase (isomerizing)
ketol acid reductoisomerase
ketol-acid reductoisomerase
(R)-2,3-dihydroxy-3-methylbutanoate:NADP+ oxidoreductase (isomerizing)
Systematic name:
(2R)-2,3-dihydroxy-3-methylbutanoate:NADP+ oxidoreductase (isomerizing)



Also catalyses the reduction of 2-ethyl-2-hydroxy-3-oxobutanoate to 2,3-dihydroxy-3-methylpentanoate. The enzyme, found in many bacteria and archaea, is specific for NADPH (cf. EC, ketol-acid reductoisomerase (NAD+) and EC, ketol-acid reductoisomerase [NAD(P)+]).

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0004455
UniProtKB/Swiss-Prot: (642) [show] [UniProt]


  1. Arfin, S.M. and Umbarger, H.E.
    Purification and properties of the acetohydroxy acid isomeroreductase of Salmonella typhimurium.
    J. Biol. Chem. 244 : 1118-1127 (1969). [PMID: 4388025]
  2. Hill, R.K., Sawada, S. and Arfin, S.M.
    Stereochemistry of valine and isoleucine biosynthesis. IV. Synthesis, configuration, and enzymatic specificity of α-acetolactate and α-aceto-α-hydroxybutyrate.
    Bioorg. Chem. 8 : 175-189 (1979).
  3. Kiritani, K., Narise, S. and Wagner, R.P.
    The reductoisomerase of Neurospora crassa.
    J. Biol. Chem. 241 : 2047-2051 (1966).
  4. Satyanarayana, T. and Radhakrishnan, A.N.
    Biosynthesis of valine and isoleucine in plants. 3. Reductoisomerase of Phaseolus radiatus.
    Biochim. Biophys. Acta 110 : 380-388 (1965). [PMID: 5866387]
  5. Brinkmann-Chen, S., Cahn, J. K., Arnold, F. H.
    Uncovering rare NADH-preferring ketol-acid reductoisomerases.
    Metab. Eng. 26C : 17-22 (2014). [PMID: 25172159]

[EC created 1972, modified 1976, modified 1981 (EC created 1972, incorporated 1976), modified 2015]