Isocitrate dehydrogenase (IDH) [PMID:2682654, PMID:1939242] is an important enzyme of carbohydrate metabolism which catalyzes the oxidative decarboxylation of isocitrate into alpha-ketoglutarate. IDH is either dependent on NAD⁺ (EC: 1.1.1.41) or on NADP⁺ (EC: 1.1.1.42). In eukaryotes there are at least three isozymes of IDH: two are located in the mitochondrial matrix (one NAD⁺-dependent, the other NADP⁺-dependent), while the third one (also NADP⁺-dependent) is cytoplasmic. In Escherichia coli the activity of a NADP⁺-dependent form of the enzyme is controlled by the phosphorylation of a serine residue; the phosphorylated form of IDH is completely inactivated.

3-isopropylmalate dehydrogenase (EC: 1.1.1.85) (IMDH) [PMID:1748999, PMID:7773180] catalyzes the third step in the biosynthesis of leucine in bacteria and fungi, the oxidative decarboxylation of 3-isopropylmalate into 2-oxo-4-methylvalerate.

Tartrate dehydrogenase (EC: 1.1.1.93) [PMID:8053675] catalyzes the reduction of tartrate to oxaloglycolate.

These enzymes are evolutionary related [PMID:2682654, PMID:1748999, PMID:7773180, PMID:8053675]. The best conserved region of these enzymes is a glycine-rich stretch of residues located in the C-terminal section.