The Enzyme Database

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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 isoleucine and valine biosynthesis, 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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