IDH1 and melanoma: Of note, the levels of the other IDHs, IDH1 and IDH2, which act in the cytoplasm and mitochondrion, respectively, as NADP (+)-dependent enzymes that similarly metabolize isocitrate to α-KG 42, were unaltered, corroborating the functional specificity of IDH3 in the metabolic switch in quiescent melanoma cells.