1. Istituto di Cristallografia, CNR, Catania 95126, Italy
2. Heidelberg University Biochemistry Center, Heidelberg 69120, Germany
3. Department of Physics, University of Helsinki, P.O. Box 64, Helsinki FI-00014, Finland
4. Institute of Organic Chemistry and Biochemistry, Prague 160 00, Czech Republic
5. Department of Chemical Sciences, University of Catania, Catania 95124, Italy
6. J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Prague 117 20, Czech Republic
7. Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
8. National Institutes of Health, Bethesda, Maryland 20892-0001, United States