1. Melvin Calvin Laboratory, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Chemistry, University of California, Berkeley, California 94720, European Synchrotron Radiation Facility, BP 220, Grenoble Cedex, France 38043, Max-Planck-Institut für Bioanorganische Chemie, D-45470 Mülheim an der Ruhr, Germany, and Stanford Synchrotron Radiation Laboratory, Menlo Park, California 94025