1. Section de Biophysique des Protéines et des Membranes, Département de Biologie Cellulaire et Moléculaire, CEA and URA 2096, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France, and Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Box 871604, Arizona State University, Tempe, Arizona 85287-1604