1. Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106-4935, Graduate Program in Biophysics, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, and Graduate Program in Molecular and Cellular Biochemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400