The COX-1 and COX-2 backbones, overlaid. COX-1 is shown in yellow, and COX-2 in pink. Note how the two structures are almost perfectly superimposable. The amphipathic helices that form the site of monotopic membrane attachment are indicated. The peroxidase (POX) active site lies on the opposite side of the molecule from the entrance to the COX active site channel. The actual position of the COX active center is marked by the asterisk, found near the center of the molecule.