ketol-acid reductoisomerase activity

Definition

Target type: molecularfunction

Catalysis of the reaction: (R)-2,3-dihydroxy-3-methylbutanoate + NADP+ = (S)-2-hydroxy-2-methyl-3-oxobutanoate + NADPH + H+. [EC:1.1.1.86]

Ketol-acid reductoisomerase (KARI) activity is a crucial step in the biosynthesis of branched-chain amino acids (BCAAs) like valine, leucine, and isoleucine. This enzyme catalyzes a two-step reaction, converting alpha-ketoisovalerate to alpha-hydroxyisovalerate, which is then isomerized to alpha-hydroxy-beta-methylbutyrate. The reaction involves the following steps:

1. **Reduction:** The enzyme utilizes NADPH as a cofactor to reduce the keto group of alpha-ketoisovalerate to a hydroxyl group, forming alpha-hydroxyisovalerate.
2. **Isomerization:** The enzyme then catalyzes the rearrangement of the hydroxyl group from the alpha to the beta position, resulting in alpha-hydroxy-beta-methylbutyrate.

This reaction is essential for BCAA biosynthesis because it converts a linear molecule (alpha-ketoisovalerate) into a branched-chain molecule (alpha-hydroxy-beta-methylbutyrate). The branched-chain structure is critical for the function of BCAAs, which play vital roles in protein synthesis, muscle growth, and energy metabolism.

Deficiency in KARI activity can lead to Maple Syrup Urine Disease (MSUD), a rare genetic disorder characterized by the accumulation of BCAAs in the body, resulting in severe neurological complications.

In summary, ketol-acid reductoisomerase activity is essential for the biosynthesis of branched-chain amino acids, a critical step in the production of essential molecules for protein synthesis and overall metabolic function.'
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Proteins (1)

Compounds (1)