Pushing the limits of flash photolysis to unravel the secrets of biological electron and proton transfer.

Time-resolved absorption spectroscopy is a powerful tool to unravel biological functions and has been a key technology for elucidating the working of electron transfer chains in photosynthesis or photorepair of UV-damaged DNA. Both of these areas have seen important contributions from laboratories all over the world, not the least of them stemming from the ingenious technical advances described by Klaus Brettel, first at the Technical University of Berlin (Germany), and later at the Atomic Energy Agency in Saclay (France). Now, after more than forty years of tireless scientific activity, Klaus is approaching retirement and this collection gathers together tributes in the form of scientific contributions from colleagues along the way, covering a spectrum of topics as diverse as photosynthesis, light-induced DNA repair, electron and proton transfer in light signalling, flavin based photo-enzymology, fluorescent marker photophysics, synthetic models and modelisation, delicate sample transient absorption spectroscopy. In an era where science is increasingly changing context from "fundamental" to "applied", Klaus' curiosity and tenacity worked hand in hand in a most effective manner to further both technical possibilities and basic understanding.

Tribute in memory of Jacques Breton (1942-2018).

Jacques Breton spent his 39 years of professional life at Saclay, a center of the French Atomic Energy Commission. He studied photosynthesis with various advanced biophysical tools, often developed by himself and his numerous coworkers, obtaining a large number of new information on the structure and the functioning of antenna and of reaction centers of plants and bacteria: excitation migration in the antenna, orientation of molecules, rate of primary reactions, binding of pigments and electron transfer cofactors. Although it is much too short to illustrate his impressive work, we hope that this contribution will help maintaining the souvenir of Jacques Breton as an active and enthusiastic person, full of qualities, devoted to research and to his family as well. We include personal comments from N. E. Geacintov, A. Dobek, W. Leibl, M. Vos and W. W. Parson.

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 tau(et) in the order of 10-50 micros), and one where electron transfer from FADH(-) (tau(et)=25 ms) is followed by reprotonation of the W306 anion.

Unraveling the photosystem I reaction center: a history, or the sum of many efforts.

This article describes some aspects of the history of the discovery of the structure and function of Photosystem I (PS I). PS I is the largest and most complex membrane protein for which detailed structural and functional information is now available. This short historical review cannot cover all the work that has been carried out over more than 50 years, nor provide a deep insight into the structure and function of this protein complex. Instead, this review focuses on more personal views of some of the key discoveries, starting in the 1950s with the discovery of the existence of two photoreactions in oxygenic photosynthesis, and ending with the race towards an atomic structure of PS I.