Read for comprehension. Catalyzed by isocitrate dehydrogenase, the oxidation of isocitrate by NAD+ converts a hydroxyl group to an aldehyde forming a β-keto acid, a species that is very susceptible to decarboxylization. The decarboxylization of this β-keto acid (oxalosuccinate) forms α-ketoglutarate. Therefore, the conversion of isocitrate to α-ketoglutarate yields NADH and CO2.