Copper electron-nuclear double resonance of cytochrome c oxidase

Electron-nuclear double resonance of copper was observed while monitoring the "intrinsic copper" electron paramagnetic resonance signal of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) near g = 2. This unambiguously establishes the presence of the metal (Cua) in the redox center responsible for this signal. The hyperfine couplings to copper are largely istropic and the maximum value is about half that seen in type I blue copper proteins. The magnetic properties of this oxidized copper center are not consistent with those of a thiyl radical (R-S) coordinated to Cu(I), and thus favor the identification of this redox center as a Cu(II) ion in a unique environment.