Mitochondrial IDP1 may regulate flux through the tricarboxylic acid cycle and respiration. Its probably critical function is the production of NADPH. D-threo-isocitrate + NADP(+) = 2-oxoglutarate + CO2 + NADPH Binds 1 Mg(2+) or Mn(2+) ion per subunit. The enzyme is subject to end product inhibition by NADPH and 2-oxoglutarate. Homodimer. By growth with glucose as a carbon source. Belongs to the isocitrate and isopropylmalate dehydrogenases family.