Peroxide Stimulated Transition Between The Ferryl Intermediates Of Bovine Cytochrome C Oxidase

During catalysis of cytochrome c oxidases (CcO) several ferryl intermediates of the catalytic heme a(3)-CuB center are observed. In the P-M ferryl state, produced by the reaction of two-electron reduced CcO with O-2, the ferryl iron of heme a(3) and a free radical are present at the catalytic center. The radical reduction stimulates the transition of the P-M into another ferryl F state. Similar ferryl states can be also generated from the oxidized CcO (O) in the reaction with H2O2. The P-M, the product of the reaction of the O with one molecule of peroxide, is transformed into the F state by the second molecule of H2O2. However, the chemical nature of this transition has not been unambiguously elucidated yet. Here, we examined the redox state of the peroxide-produced P-M and F states by the one-electron reduction. The F form and interestingly also the major fraction of the P-M sample, likely another P-type ferryl form (PR), were found to be the one oxidizing equivalent above the O state. However, the both P-type forms are transformed into the F state by additional molecule of H2O2. It is suggested that the PR-to-F transition is due to the binding of H2O2 to CuB triggering a structural change together with the uptake of H+ at the catalytic center. In the P-M-to-F conversion, these two events are complemented with the annihilation of radical by the intrinsic oxidation of the enzyme.