D-threo-isocitrate + NADP(+) = 2-oxoglutarate + CO2 + NADPH Binds 1 Mg(2+) or Mn(2+) ion per subunit. Homodimer. The enzyme can be phosphorylated in vitro by the E.coli isocitrate dehydrogenase kinase/phosphatase, but B.subtilis lacks such an enzyme. Belongs to the isocitrate and isopropylmalate dehydrogenases family.