1. Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721, Laboratory of Protein Biochemistry and Protein Engineering, Ghent University, K. L. Ledeganckstraat 35, 9000 Ghent, Belgium, Department of Chemistry, Chosun University, Kwangju 501-759, Korea, and Biophysics Group, Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany