Isocitrate/isopropylmalate dehydrogenase family
In molecular biology, the isocitrate/isopropylmalate dehydrogenase family is a protein family consisting of the evolutionary related enzymes isocitrate dehydrogenase, 3-isopropylmalate dehydrogenase and tartrate dehydrogenase. Isocitrate dehydrogenase (IDH), is an important enzyme of carbohydrate metabolism which catalyses the oxidative decarboxylation of isocitrate into alpha-ketoglutarate. IDH is either dependent on NAD or on NADP . 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 (IMDH) catalyses 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 catalyses the reduction of tartrate to oxaloglycolate.