1. Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, Department of Information Systems Engineering, Faculty of Engineering, Osaka Sangyo University, Daito, Osaka 574, Japan, and Chemistry Department, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands