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