OXYGEN-BINDING AND ACTIVATION - EARLY STEPS IN THE REACTION OF OXYGENWITH 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 firs t 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 ti me constants of 8 and 32 mu s and to separate their spectra. The spect rum of the first phase is comparable to that of oxygen binding to myog lobin, while the spectrum of the second phase appears to contain a con tribution from a peroxy intermediate. The results are discussed in the context of a model in which the 8-mu s phase reflects the establishme nt of an equilibrium of oxygen-bound states, while the 32-mu s phase a rises when this system is trapped as a peroxy intermediate, by inter-h eme electron transfer.