X-ray absorption edge studies on oxidized and reduced cytochrome c oxidase

The x-ray absorption edge spectra of the Cu and Fe centers in oxidized and reduced cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase; EC 1.9.3.1) have been obtained using synchrotron radiation from the SPEAR storage ring at the Stanford Linear Accelerator Center. In addition, oxidized and reduced plastocyanin as well as a number of model copper compounds in various oxidation states were also examined. A comparison of the absorption edge fine structure of cytochrome oxidase with those of the models indicates that one of the two coppers in the oxidized protein is in the + 1 oxidation state. Upon reduction of the protein with dithionite, the second copper becomes Cu(I). The shift in the Fe K-edge of cytochrome oxidase upon reduction is small (about 2 eV or 3 x 10(-19) J) and is comparable to that previously observed for the reduction of the heme iron of cytochrome c