1. Chemistry, Materials, Life and Earth Sciences Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, L-233, Livermore, California 94550, University of California, Davis, Davis, California 95817, Biochemisches Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland, Physikalische Biochemie, Universität Potsdam, 14476 Potsdam-Golm, Germany, and Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung, 12489 Berlin, Germany