Bell-shaped dependence of the rate of ultrafast photoinduced electron transfer from aromatic amino acids to the excited flavin on the donor-acceptor distance in FMN binding proteins

The ultrafast fluorescence dynamics of WT, and the E13K, E13R, E13T and E13Q substitution isoforms of FMN binding protein (FBP) were simultaneously analyzed with molecular dynamics simulation structures and an ET theory. A bell-shape behavior of the logarithmic ET rates from Trp32 and Trp106 to Iso∗ versus the centre-to-centre donor-acceptor distances (Rc) was obtained in the time domain of sub-ps to ps in all FBP isoforms. The nuclear term in the ET theory is important in the ultrafast time domain, whereas the electronic coupling term may be dominant in the slower ET rates.