1. Contribution from the Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802, Department of Biochemistry, Molecular Biology, and Cell Biology and Department of Chemistry, Northwestern University, Evanston, Illinois 60208, Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, Portland, Oregon 97006-8921, Department of Physics, Emory University, Atlanta, Georgia 30322, and Department of Chemistry...