Kinetics of electron transfer in the bc1 complex

by Durham, Bill; Havens, Jeffrey; Yang, Shaoqing; Yu, Chang-An; Yu, Linda; Millett, Frank

The kinetics of electron transfer in cytochrome bc1 has been investigated using laser flash photolysis initiated by excitation of ruthenium(II) polypyridyl complexes. The ruthenium complex binds to cytochrome bc1 at or very near to the cytochrome c binding site. Excitation at 480 nm with a short laser pulse results in rapid electron transfer (< 1 usec) from cytochrome c1 to the ruthenium complex. Subsequent internal electron transfers were monitored using a fast CCD camera to record the changes in the visible spectra. Addn. of one equiv. of antimycin, an inhibitor of the Qi site, showed no effect on the oxidn. of the heme bH. Further addn., up to a total of two equiv., resulted in a decrease in the extent of oxidn. of the heme bH. These observations are interpreted as an indication of electron transfer across the hemes bL with a rate const. of at least 500 s-1.