ABSTRACT
The active site in resting cytochrome c oxidase lies at the iron(III)/copper(II) oxida tion level. Incubation of CcO with carbon monoxide allows the active site of the enzyme to be clamped in its fully reduced iron(II)/copper(I) state. Photolysis of this inhibited enzyme ejects the CO ligand from the active site, transiently generating fully reduced CcO, whose reaction with dioxygen has been extensively probed using time-resolved resonance Raman [205] and UV-Vis spectroscopies [93]. Exposure of fully reduced CcO to dioxygen first generates “A-CcO” , which is believed to contain a simple iron/dioxygen adduct analogous to that in oxy-hemoglobin; CuB is still reduced in this form. A-CcO then transforms into the “ P” -state, which in turn decays first to the “ F” state, then to a final “ H” -state (Fig. 11). The P and F states of the active site can also be produced by treatment of fully oxidized CcO with hydrogen peroxide or of partially oxidized enzyme with dioxygen [206-208].
