The EPR spectrum for CuB in cytochrome c oxidase

Incubation of cytochrome c oxidase (CcO) in its resting state in saturated ammonium sulfate, at room temperature overnight, gave EPR signals characteristic of a single Cu(II) center. From the g// and A// values it is concluded that this is a square-planar type 2 copper center, and superhyperfine splitting shows the presence of three nearly equivalent 14N nuclei in the plane. It is suggested that this center, also formed by incubating the enzyme in 10% methanol followed by direct irradiation, must be the CuB center. This type 2 copper EPR spectrum is identical to the EPR spectrum of CuB reported for the isolated cytochrome bo3 complex from Escherichia coli; and to the EPR spectrum reported for the sulfobetaine 12 heat-treated cytochrome c oxidase complex. It is argued that a small perturbation in the system causes decoupling of the magnetic coupling of the heme a3-CuB binuclear center and the appearance of the type 2 EPR signal.