3-Isopropylmalate dehydratase, small subunit; Catalyzes the isomerization between 2-isopropylmalate and 3- isopropylmalate, via the formation of 2-isopropylmaleate. Belongs to the LeuD family. LeuD type 1 subfamily.

Acetolactate synthase is a complex of a large catalytic chain and a small regulatory chain associated in an alpha2/beta2 heterotetramer. It catalyzes the first step of the isoleucine and valine biosynthesic pathways. The catalytic subunit, IlvB, is a thiamine pyrophosphate-dependent enzyme. It also binds one magnesium ion and one FAD per subunit, although the role of this cofactor is not clear considering that the reaction does not involve redox chemistry; Localized in the cytoplasm; High confidence in function and specificity.

Acetolactate synthase is a complex of a large catalytic chain and a smaller regulatory chain associated in an alpha2/beta2 heterotetramer. It catalyzes the first step of the isoleucine and valine biosynthesic pathways. The regulatory subunit, IlvH, features an ACT domain. ACT domains are linked to a wide range of metabolic enzymes that are regulated by amino acid concentration; Localized in the cytoplasm; High confidence in function and specificity.

Threonine dehydratase; Catalyzes the anaerobic formation of alpha-ketobutyrate and ammonia from threonine in a two-step reaction. The first step involved a dehydration of threonine and a production of enamine intermediates (aminocrotonate), which tautomerizes to its imine form (iminobutyrate). Both intermediates are unstable and short-lived. The second step is the nonenzymatic hydrolysis of the enamine/imine intermediates to form 2- ketobutyrate and free ammonia. In the low water environment of the cell, the second step is accelerated by RidA.

3-Isopropylmalate dehydrogenase; Catalyzes the oxidation of 3-carboxy-2-hydroxy-4- methylpentanoate (3-isopropylmalate) to 3-carboxy-4-methyl-2- oxopentanoate. The product decarboxylates to 4-methyl-2 oxopentanoate. Belongs to the isocitrate and isopropylmalate dehydrogenases family.

2-Isopropylmalate synthase catalyzes the first step in the L-leucine biosynthesis pathway. LeuA condensates the acetyl group of acetyl-CoA with 3-methyl-2- oxobutanoate (2-oxoisovalerate) to form 3-carboxy-3-hydroxy-4-methylpentanoate (2-isopropylmalate). Its features a N-terminal catalytic HMGL-like domain and a C-terminal LeuA-dimerization domain. LeuA forms a homotetramer. Localized in the cytoplasm; High confidence in function and specificity; Belongs to the alpha-IPM synthase/homocitrate synthase family.

2-Isopropylmalate synthase catalyzes the first step in the L-leucine biosynthesis pathway. LeuA condensates the acetyl group of acetyl-CoA with 3-methyl-2- oxobutanoate (2-oxoisovalerate) to form 3-carboxy-3-hydroxy-4-methylpentanoate (2-isopropylmalate). LeuA2 is a paralogue of leuA1 which misses the C-terminal LeuA-dimerization domain. Localized in the cytoplasm; Specificity unclear; Belongs to the alpha-IPM synthase/homocitrate synthase family.

Dihydroxy-acid dehydratase catalyzes the fourth step in the biosynthesis of isoleucine and valine, the dehydratation of 2,3-dihydroxy-isovaleic acid into alpha-ketoisovaleric acid; Binds a 4Fe-4S cluster; Localized in the cytoplasm; High confidence in function and specificity; Belongs to the IlvD/Edd family.

Dihydroxy-acid dehydratase catalyzes the fourth step in the biosynthesis of isoleucine and valine, the dehydratation of 2,3-dihydroxy-isovaleic acid into alpha-ketoisovaleric acid; Binds a 4Fe-4S cluster; Localized in the cytoplasm; High confidence in function and specificity; Belongs to the IlvD/Edd family.