Energy vs Electron Transfer Tryptophan-to-Heme in Cytochrome C

The goal of this proposal is to explore the competition between electron and energy transfer from photoexcited tryptophan to the heme group in ferrous and ferric Cytochrome c in physiological media. Cyt c contains only one tryptophan amino-acid residue, whose decay is still debated. While previous works alluded to an energy transfer, our recent experimental and theoretical studies raise the question of a competing electron transfer process, possibly simultaneous to a back-electron transfer in a Dexter process. This question can be resolved by monitoring the response of the central iron atom via femtosecond X-ray emission and X-ray absorptions, only possible due to the high peak brightness and short pulse duration of x-ray FELs.