1. Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, Institute for Neurodegenerative Diseases and Departments of Neurology and of Biochemistry and Biophysics, University of California, San Francisco, California 94143, and Biophysics Research Institute, Medical College of Wisconsin, Milwaukee, Wisconsin 53226