OXYGEN-BINDING AND ACTIVATION - EARLY STEPS IN THE REACTION OF OXYGEN WITH CYTOCHROME-C-OXIDASE

We have studied the flow-flash reaction of fully reduced cytochrome c oxidase with a high concentration of oxygen (1 mM), recording the first 200 mu s of the reaction at a number of wavelengths between 400 and 455 nm. This approach has allowed us to observe kinetic phases with time constants of 8 and 32 mu s and to separate their spectra. The spectrum of the first phase is comparable to that of oxygen binding to myoglobin, while the spectrum of the second phase appears to contain a contribution from a peroxy intermediate. The results are discussed in the context of a model in which the 8-mu s phase reflects the establishment of an equilibrium of oxygen-bound states, while the 32-mu s phase arises when this system is trapped as a peroxy intermediate, by inter-heme electron transfer.