Photoinduced intracomplex electron transfer between cytochrome c oxidase and TUPS-modified cytochrome c

A novel method for initiating intramolecular electron transfer in cytochrom e c oxidase is reported. The method is based upon photoreduction of cytochr ome c labeled with thiouredopyrene-3,6,8-trisulfonate in complex with cytoc hrome oxidase. The thiouredopyrene-3,6,8-trisulfonate-labeled cytochrome c was prepared by incubating the thiol reactive form of the dye with yeast is o-l-cytochrome c, containing a single cysteine residue. Laser pulse excitat ion of a stoichiometrical complex between thiouredopyrene-3,6,8-trisulfonat e-cytochrome c and bovine heart cytochrome oxidase at low ionic strength re sulted in the reduction of cytochrome c by the excited form of thiouredopyr ene-3,6,8-trisulfonate and subsequent intramolecular electron transfer from the reduced cytochrome c to cytochrome oxidase. The maximum efficiency by a single laser pulse resulted in the reduction of approximate to 17% of cyt ochrome a, and was achieved only at a 1 : 1 ratio of cytochrome c to cytoch rome oxidase. At higher cytochrome c to cytochrome oxidase ratios the heme a reduction was strongly suppressed.