1. Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118, Institut für Biophysikalische Chemie, Johann Wolfgang Goethe-Universität, 60439 Frankfurt am Main, Germany, Phoenix Epidemiology and Clinical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona 85016, and Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77845