Both monomeric and dimeric NADPþ-dependent isocitrate dehydrogenases (IDHs) belong to the metal-dependent b-decarboxylating dehydrogenase family and catalyze the oxidative decarboxylation from 2R,3S-isocitrate to yield a-ketoglutarate, CO2, and NADPH. However, the biochemical analyses, crystal structures and catalytic mechanism of monomeric IDH are not yet well known as dimeric IDH