1. Laboratory
of Chemical Physics, National Institute of Diabetes and Digestive
and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, United States
2. Department
of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
3. National Institute of Standards and Technology and the Institute for Bioscience and Biotechnology Research, Rockville, Maryland 20850, United States