D-threo-isocitrate + NADP(+) = 2-oxoglutarate + CO2 + NADPH Binds 1 Mg(2+) or Mn(2+) ion per subunit. Weakly inhibited by oxaloacetate, 2-oxoglutarate, and citrate. Severely inhibited by oxaloacetate plus glyoxylate. Monomer. Belongs to the monomeric-type IDH family.