1. Centre for Metals in Biology, School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Qld 4072, Australia, CCLRC Daresbury Laboratory, Warrington WA4 4AD, U.K., Department of Chemistry, University of Arizona, Tucson, Arizona 85721, Centre for Magnetic Resonance, The University of Queensland, Brisbane, Qld 4072, Australia, and Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721