1. Contribution from the Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K., Institut für Biologie/Mikrobiologie, Humboldt-Universität zu Berlin, Chausseestrasse 117, 10115 Berlin, Germany, Swammerdam Institute for Life Sciences, University of Amsterdam, Nieuwe Achtergracht 166, NL-1018 WV Amsterdam, The Netherlands, Laboratoire de Cristallographie et de Cristallogenèse des Protèines, Institut de Biologie Structurale J.P. Ebel (CEA-CNRS-UJF), 41 rue Jules Horowitz,...