The P intermediates of cytochrome c oxidase from Paracoccus denitrificans

Cytochrome c Oxidase (CcO) is one of the most fundamental enzymes of life in its present form. As the terminal enzyme of the respiratory chain, this redox driven proton pump catalyzes the four electron reduction of molecular oxygen to water and couples this exergonic reaction to the generation of an electrochemical proton gradient across the membrane into which it is embedded. Elucidation of the structures of intermediates in the catalytic cycle is crucial for understanding both the mechanism of oxygen reduction and its coupling to proton pumping. We report on the preparation as well as the UV/visible and EPR spectroscopic characterization of various and also new artificial intermediates of CcO closely related to the P intermediate, one of the key states usually observed in the catalytic cycle of CcO.

Treatment of the hydrogen peroxide derived F state with ammonia is suggested to lead by coordination of ammonia to Cu_B to the formation of the new P_N state [1]. In particular the relation of the amino acid radical at residue Y167 (P. denitrificans numbering), present in some artificial intermediates, and the natural catalytic cycle is discussed.