1. Department
of Chemistry, University of Michigan, Box
1055, Ann Arbor, Michigan 48109, United States
2. Department of Chemistry, Duke University, Box 90317, Durham, North Carolina 27708,
United States
3. Department
of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, United States
4. Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109,
United States