The docking calculations are also performed on a primary drug metabolizing human liver enzyme P450, CYP 3A4. This enzyme is one of 6 CYP enzymes responsible for extracting waste-like molecules from the human body. CYP 3A4, while being considered the most prevalent, is one of these. The crystal structure of Ritonavir bound to CYP 3A4 was used in the docking calculations, with the ligand stripped. The binding site of CYP 3A4 is a large vacuous chamber on one side of the heme iron atomic frame. CYP 3A4's binding site will stick highly to very general molecules. Because of its size geometrically, larger small molecules can easily 'fit' into this region without obstruction which is presumably why this enzyme is good at transporting waste molecules from the liver. A total ligand-protein binding energy will scale with the number of heavy atoms, so that a bound small molecule twice the size of another could result in a larger, even ~2x, larger binding energy. However, the target protein binding site of the drug is amino acid specific in function and increasing the size can miss the target and also create unwanted interactions with other proteins.