Ketol-acid reductoisomerase (NADP(+))

UniProtKB accession:  P05793

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UniProtKB description:  Involved in the biosynthesis of branched-chain amino acids (BCAA). Catalyzes an alkyl-migration followed by a ketol-acid reduction of (S)-2-acetolactate (S2AL) to yield (R)-2,3-dihydroxy-isovalerate. In the isomerase reaction, S2AL is rearranged via a Mg-dependent methyl migration to produce 3-hydroxy-3-methyl-2-ketobutyrate (HMKB). In the reductase reaction, this 2-ketoacid undergoes a metal-dependent reduction by NADPH to yield (R)-2,3-dihydroxy-isovalerate. Also able to use 2-ketopantoate, 2-ketoisovalerate, 2-ketovalerate, 2-ketobutyrate, 3-hydroxypyruvate, 3-hydroxy-2-ketobutyrate and pyruvate (PubMed:15654896).