1. Department of Physical Chemistry, Eötvös University, H-1117 Budapest, Pázmány P. sétány 1/A, Hungary, Faculty of Medicine, Institute of Biophysics and Radiation Biology, Semmelweis University, H-1444 Budapest, Puskin u. 9, POB 263, Hungary, and Institute of Molecular and Biological Chemistry, Swiss Federal Institute of Technology Lausanne, EPFL-BCH, CH-1015 Lausanne, Switzerland