Oxygen activation and reduction in respiration: Involvement of redox-active tyrosine 244

Cytochrome oxidase activates and reduces O-2 to water to sustain respiratio n and uses the energy released to drive proton translocation and adenosine 5'-triphosphate synthesis. A key intermediate in this process, P, lies at t he junction of the O-2-reducing and proton-pumping functions. We used radio active iodide labeling followed by peptide mapping to gain insight into the structure of P. We show that the cross-linked histidine 240-tyrosine 244 ( His(240)-Tyr(244) species is redox active in P formation, which establishes its structure as Fe-IV=O/(CuB2+H240)-Y-244. Thus, energy transfer from O-2 to the protein moiety is used as a strategy to avoid toxic intermediates a nd to control energy utilization in subsequent proton-pumping events.