1. College of Pharmacy, University of New Mexico, Albuquerque, New Mexico 87131, Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721, Department of Medicine, Duke University and VA Medical Centers, Durham, North Carolina 27705, Department of Biology, Rensselaer Polytechnic Institute, Troy, New York 1485, and Department of Chemistry, University of Arizona, Tucson, Arizona 85721