Copper electron-nuclear double resonance of cytochrome c oxidase.

Abstract
Electron-nuclear double resonance of Cu was observed while monitoring the intrinsic Cu EPR signal of [beef heart mitochondria] cytochrome c oxidase (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 Cu are largely isotropic and the maximum value is about half that seen in type I blue Cu proteins. The magnetic properties of this oxidized Cu center are not consistent with those of a thiyl radical (R.sbd.S.cntdot.) coordinated to Cu(I), and thus favor the identification of this redox center as a Cu(II) ion in a unique environment.

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