1. Institut für Biophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany.
2. Departments of Biology and Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
3. ules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90024-7008, USA.
4. Central Research Laboratory, Chemistry, University of P6cs, H-7643 Pécs, Hungary.