The proteins with PDB codes 1k71 and 1k74 were chosen for modeling. In addition to the available knowledge of their 3D (dimensional) structures, the reasons of selecting the two proteins as receptors are as follows. (1) The two proteins contain the same ligand GW409544 as PPARa and PPARc do, and their binding affinities with the ligand are also quite similar; however, the former selectivity is about 10-fold weaker than the latter [37] . (2) The source organism of both PPARa and PPARc was from human.