Electron spin echo studies of cytochrome c oxidase.

We have studied the linear electric field effect in pulsed EPR of the "EPR-detectable copper" signal of beef heart cytochrome c oxidase and have compared our results with those for a variety of square planar and tetrahedral Cu(II) model compounds and with Cu(II) proteins containing either type 1 or type 2 copper. The electric field induced g shifts (linear electric field effect) for cytochrome oxidase are comparable in magnitude to those for simple Cu(II) complexes and for some copper proteins containing type 2 sites. The shifts are smaller than those for tetrahedral copper complexes and for type 1 copper sites. However, the magnetic field dependence of the linear electric field effect does not resemble that observed for any Cu(II) complex studied nor for type 1 copper. These findings cannot be reconciled with the tetrahedral Cu(II) model proposed by Greenaway, Chan, and Vincow ((1977) Biochim. Biophys. Acta 490, 62-78, 1977) to explain the unusual EPR spectrum of cytochrome oxidase.