Isocitrate dehydrogenase (IDH) from the hyperthermophile Thermotoga maritima(TmIDH) catalyses NADP + - and metal-dependent oxidative decarboxylation of isocitrate toa-ketoglutarate. It belongs to the b-decarb-oxylating dehydrogenase family and is the only hyperthermostable IDH identified within subfamily II. Furthermore, it is the only IDH that has been characterized as both dimeric and tetrameric in solution.