Function of Bovine Heart Cytochrome c Oxidase

Long before the erystal structure of cytochrome c oxidase was solved, the function of this enzyme had already been investigated by using the transition metal sites as spectroscopic probes (Caughey et al., 1976 Malmstr m, 1990 Ferguson-Miller and Babcock, 1996). The information obtained from these spectroscopic investigations initiated prior to the crystal structure determination will be summarized. 

It is important to recognize that a complete initial steady state kinetic analysis of the cytochrome c oxidase reaction has yet to be undertaken. The complete set of enzyme reactants includes four ferrocytochrome c molecules and one O2 molecule as substrates, and because of the extremely low 

Km of the enzyme for O2, This system is not easily amenable to steady state kinetic analysis. As has been widely demonstrated, initial steady state kinetic analysis provides a variety of unique information about the function of enzymes impossible to obtain from other methods (Cleland, 1970). 

The transfer of electrons to heme a3 from ferrocytochrome c in the fully oxidized enzyme under anaerobic conditions in an atmosphere of CO was monitored by following development of photosensitivity due to formation of the CO complex (Gibson et al., 1965). Surprisingly, the photosensitivity appeared within a timeframe of one second, which is 10 times slower than the electron transfer to heme a3 from heme a in the reaction of the fully reduced enzyme with O2 (Hill, 1994). On the other hand, Brunori and his coworkers discovered that the enzyme molecules in the preparation 

Although this mechanism has been widely accepted, an important point suggested by this mechanism is not well understood. The formation of the p,-peroxo intermediate (Fe oOoOoCu ) is likely to be extremely rapid, since this reaction step is limited by the rate of electron transfer from Cug to one of the oxygen atoms of the bound O2. Electron transfer rates for such a short distance (about 2 ) could be as fast as a pico second. On 

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