Background：Isocitrate dehydrogenases catalyze the oxidative decarboxylation of isocitrate to 2-oxoglutarate. These enzymes belong to two distinct subclasses, one of which utilizes NAD（+） as the electron acceptor and the other NADP（+）. Five isocitrate dehydrogenases have been reported： three NAD（+）-dependent isocitrate dehydrogenases, which localize to the mitochondrial matrix, and two NADP（+）-dependent isocitrate dehydrogenases, one of which is mitochondrial and the other predominantly cytosolic. NAD（+）-dependent isocitrate dehydrogenases catalyze the allosterically regulated rate-limiting step of the tricarboxylic acid cycle. Each isozyme is a heterotetramer that is composed of two alpha subunits, one beta subunit, and one gamma subunit.
