IUBMB Enzyme Nomenclature


Accepted name: ketol-acid reductoisomerase (NADP+)

Reaction: (2R)-2,3-dihydroxy-3-methylbutanoate + NADP+ = (2S)-2-hydroxy-2-methyl-3-oxobutanoate + NADPH + H+

For diagram of reaction click here.

Glossary: (2S)-2-hydroxy-2-methyl-3-oxobutanoate = (2S)-2-acetolactate

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

Systematic name: (2R)-2,3-dihydroxy-3-methylbutanoate:NADP+ oxidoreductase (isomerizing)

Comments: 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: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9075-02-9


1. Arfin, S.M. and Umbarger, H.E. Purification and properties of the acetohydroxy acid isomeroreductase of Salmonella typhimurium. J. Biol. Chem. 244 (1969) 1118-1127. [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 (1979) 175-189.

3. Kiritani, K., Narise, S. and Wagner, R.P. The reductoisomerase of Neurospora crassa. J. Biol. Chem. 241 (1966) 2047-2051.

4. Satyanarayana, T. and Radhakrishnan, A.N. Biosynthesis of valine and isoleucine in plants. 3. Reductoisomerase of Phaseolus radiatus. Biochim. Biophys. Acta 110 (1965) 380-388. [PMID: 5866387]

5. Brinkmann-Chen, S., Cahn, J.K. and Arnold, F.H. Uncovering rare NADH-preferring ketol-acid reductoisomerases. Metab. Eng. 26C (2014) 17-22. [PMID: 25172159]

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

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