Application of metal complex mediated laser flash photolysis to the investigation of the electron transfer pathway in cytochrome bc1

by Havens, Jeffrey Allen; Yang, Shaoqing; Yuan, Quan; Yu, Chang-An; Yu, Linda; Durham, Bill; Millett, Francis Spencer

Electron transfer in R. Sphaeroides cytochrome bc1 has been investigated using laser flash photolysis mediated by a ruthenium dimer, (bpy)2RuqpyRu(bpy)24+. The ruthenium complex binds to cytochrome bc1 at a location similar to that used by cytochrome c. 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 at wavelengths specific to each reaction. For example, electron transfer from the ISP to heme c1 was biphasic with rates consts. of 80,000 s-1 and 3500 s-1. Overall kinetic measurements suggest that the quinone produced at the Qo site diffuses through the complex to Qi site and that electrons are transferred across the hemes bL with a rate const. of at least 500 s-1. Use of a new inorg. complex based on Cr(bpy)33+ as a photoinitiator will also be described.