Experiment title: Time-resolved diffuse x-ray scattering studies of a photosynthetic reaction centre and bacterial rhodopsins Experiment number: CH2271 Beamline: ID09B Date of experiment: from: 7 th July 2007 to: 9 th July 2007 Date of report: 25/08/2007 Shifts: 9 Local contact(s): Dr. Marco CAMMARATA Received at ESRF: Names and affiliations of applicants (* indicates experimentalists): Annemarie Wöhri 1* , Magnus Andersson 2* , Erik Malmerberg 2* , Emily Fritz 2* , Richard Neutze 2* , Mattias Eklund 3* , Jan Davdisson 3* 2 Department of Physical Chemistry, Uppsala University. 1 Department of Chemistry & Bioscience, Chalmers University of Technology. Department of Chemistry, Biochemistry & Biophysics, Göteborg University Report: This experiment was carried forward from the previous allocation period, since technical problems at ID09 of the ESRF meant that it was not possible to schedule this experiment during the last run. Although at the time we foresaw a first experiment on the diffuse x-ray method for membrane proteins, which we had developed for simple photochemical systems [1,2], the emergence of a new crystal form of the R. viridis reaction centre made Laue diffraction studies a higher priority. We therefore made the decision, after consultation with Dr. Michael Wulff (beamline scientist for ID09), to prioritise a continuation of Laue diffraction studies of the reaction centre. This turned out to be a very good decision since the project made a tremendous jump forward. We now have scheduled time for the first liquid phase experiment in September 2007 (CH-2521). Background Photosynthetic organisms thrive by generating chemiosmotic potential across their biological membranes. One such bacterium is Rhodopseudomonas viridis in which light-driven reactions take place in a membrane- bound protein complex called the reaction centre (RC). When a photon is absorbed by the special pair (P) in the RC an electron transfer reaction is initiated across the membrane which ultimately leads to the reduction of a ubiquinone molecule (Q B ). The ubiquinone molecule diffuses in the membrane to the cytochrome bc 1 complex which oxidises it in two steps on the other side of the membrane. This so called redox loop is responsible for the active translocation of protons across the membrane. As a consequence a proton gradient is maintained and the energy stored in this gradient is harvested to propel vitally important reactions. One such example is the synthesis of ATP, the universal energy currency of the cell, which is primarily synthetised by the ATPsynthase utilising the chemiosmotic potential of H + ions.