1. School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K., Centre for Biomolecular Sciences, University of St. Andrews, St. Andrews, Scotland, Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310-4005, and Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32310