The Role of Magnesium and Its Associated Water Channel in Activity and Regulation of Cytochrome cOxidase

Research on cytochrome coxidase has moved into a new era with the recent resolution of the crystal structures of bacterial [1] and beef heart [2] enzymes, showing their remarkable similarity. The resolution of the crystal structures has specified the spatial organization of the metal centers and defined some possible routes for proton translocation within the molecule. Three distinct pathways for protons are expected in the cytochrome coxidase: two entries for the pumped and substrate protons and an unidirectional exit route. An apparent water channel, which could function as the proton exit pathway, is clearly visible in the beef heart oxidase X-ray structure [2] (Figure 1): it is immediately above the active site and connects it to the exterior of the membrane.