Photoinitiated Electron Transfer between Cytochrome c and Cytochrome c Oxidase Using a Novel Uroporphyrin/NADH Reducing System

Article abstract of DOI:10.1021/j100199a036

We have employed a novel photoreduction system to investigate the electron-transfer reaction between cytochrome c and cytochrome c oxidase.In this system, the photogenerated uroporphyrin triplet state is quenched through electron transfer to ferricytochrome c.The corresponding uroporphyrin ?-cation radical is rapidly reduced by nicotonamid adenine dinucleotide (NADH) resulting in the in situ generation of ferrocytochrome c.In the presence of cytochrome c oxidase, cytochrome c is reoxidized biphasically while the corresponding reduction of cytochrome a appears to be monophasic.In addition, the fast-phase rate constants are dependent upon the concentration of cytochrome c oxidase giving a first-order intracomplex electron-transfer rate constant, (k_et), of 1829 +/-248 s^-1.The ratio of electron transferred from ferrocytochrome c to cytochrome a is 1:1 indicating that cytochrome a is the ultimate acceptor of the electrons.