1. Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110
2. Department of Physics, Washington University, St. Louis, MO 63130
3. Center for Neutron Research, National Institute for Standards and Technology, Gaithersburg, MD 20899
4. Theoretical Molecular Biophysics Laboratory, National Heart, Lung and Blood Institute, NIH, Bethesda, MD 20894
5. Department of Molecular Physiology and Biophysics, The University of Iowa, Iowa City, IA 52242