1. ReQuimte, Centro de Química Física e Biotecnologia, FCT/UNL, Quinta da Torre, 2829-516 Caparica, Portugal, Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Summerhall, Edinburgh, EH9 1QH, Scotland, U.K., Unité de Bioénergétique et Ingénierie des Protéines, IBSM-CNRS, 31 Chemin Joseph Aiguier, 13402, Marseille Cedex 20, France, and Laboratory of Protein Biochemistry, State University of Gent, B-9000 Gent, Belgium