1. Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, Molecular Neurobiology Laboratory, Department of Preventive Sciences, University of Minnesota Dental School, Minneapolis, Minnesota 55417, Department of Chemistry, Boston University, Boston, Massachusetts 02215, and Department of Pathology & Laboratory Medicine (Neuropathology) and Brain Research Institute, University of California, Los Angeles Medical Center, Los Angeles, California 90095