Isocitrate dehydrogenase (NAD+) (, isocitric dehydrogenase, beta-ketoglutaric-isocitric carboxylase, isocitric acid dehydrogenase, NAD dependent isocitrate dehydrogenase, NAD isocitrate dehydrogenase, NAD-linked isocitrate dehydrogenase, NAD-specific isocitrate dehydrogenase, NAD isocitric dehydrogenase, isocitrate dehydrogenase (NAD), IDH (ambiguous), nicotinamide adenine dinucleotide isocitrate dehydrogenase) is an enzyme with systematic name isocitrate:NAD+ oxidoreductase (decarboxylating). This enzyme catalyses the following chemical reaction
It requires Mn<sup>2+</sup> or Mg<sup>2+</sup> for activity. Unlike EC 1.1.1.42, isocitrate dehydrogenase (NADP<sup>+</sup>), oxalosuccinate cannot be used as a substrate. In eukaryotes, isocitrate dehydrogenase exists in two forms: an NAD<sup>+</sup>-linked enzyme found only in mitochondria and displaying allosteric properties, and a non-allosteric, NADP<sup>+</sup>-linked enzyme that is found in both mitochondria and cytoplasm. The enzyme from some species can also use NADP<sup>+</sup> but much more slowly.