Isocitrate dehydrogenase (IDH) is an enzyme with two protein subunits. Three different isocitrate dehydrogenases are present: one specific for NAD⁺, found only in mitochondria and the other two specific for NADP⁺, found in mitochondria and cytoplasm. The main role of isocitrate dehydrogenase is to convert isocitrate into oxalosuccinate with the help of NAD⁺ or NADP⁺  and Mg⁺² or Mn⁺².

Isocitrate, produced from the isomerization of citrate, is held within its active site using the enzyme isocitrate dehydrogenase (IDH). 

Oxidation is the first step where the hydroxyl group of the α carbon of the isocitrate is deprotonated using NAD⁺ or NADP⁺  as an electron accepting cofactor. During this process, a hydrogen ion is released to form a ketone group. The oxidation of the α carbon enables the electrons to come down to a position from the carboxyl group and the electrons are pushed up back on the oxygen.

Next, the unstable oxalosuccinate undergoes β decarboxylation and as a result, the CO₂ that is produced during the reaction, is given out and hydrogen is added to the β carbon. Thus, the final product, α-ketoglutarate is formed.