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

Abstract : 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 In addition, we present unpublished data on the charge recombination between the fully reduced FADH- and the neutral (deprotonated) radical of the solvent exposed tryptophan W306.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 (kH/kD=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 tet in the order of 10-50 µs), and one where electron transfer from FADH- (tet=25 ms) is followed by reprotonation of the W306 anion. Cop. 2004 Elsevier B.V. All rights reserved.