1. School of Chemistry, University of Sydney, Sydney NSW 2006, Australia, School of Molecular and Microbial Biosciences, University of Sydney, Sydney NSW 2006, Australia, Department of Physiology and Biophysics, University of Aarhus, DK-8000 Aarhus C, Denmark, Faculty of Biology, University of Konstanz, D-78435 Konstanz, Germany, and Laboratoire de Chimie-Physique, Université Paris-Sud/CNRS, F-91405 Orsay, France