Energy transfer and relaxation mechanisms in Cytochrome c

Using broadband UV–vis femtosecond transient absorption and fluorescence up-conversion, we investigate the interaction between the haem moiety of ferric and ferrous Horse heart Cytochrome c and its single Tryptophan (Trp) residue and the energy dissipation mechanisms upon excitation at various wavelengths in the visible and the UV. Varying the amount of energy deposited in the haem does not affect the relaxation and cooling processes. Differences are observed between the cooling time-scales of the two redox states, which are attributed to different haem–protein couplings. While energy transfer from the Trp to the haem is observed in the decay of Trp and the response of the haem, excitation of the latter does not induce a clear response of the former. This suggests that for Cytochrome c, Trp is not a good marker of the protein response, probably due to its orientation with respect to the haem plane.