Intraprotein electron transfer and proton dynamics during photoactivation of DNA photolyase from E. coli: Review and new insights from an "inverse" deuterium isotope effect

We review our work on electron transfer and proton dynamics during photoactivation in DNA photolyase from E. coli and discuss a recent theoretical study on this issue. In addition, we present unpublished data on the charge recombination between the fully reduced FADH^- and the neutral (deprotonated) radical of the solvent exposed tryptophan W306. We found a pronounced acceleration with decreasing pH and an inverse deuterium isotope effect (k_H/k_D=0.35 at pL 6.5) and interpret it in a model of a fast protonation equilibrium for the W306 radical. Due to this fast equilibrium, two parallel recombination channels contribute differently at different pH values: one where reprotonation of the W306 radical is followed by electron transfer from FADH^- (electron transfer time constant τ_et in the order of 10-50 μs), and one where electron transfer from FADH^- (τ_et=25 ms) is followed by reprotonation of the W306 anion.