1. Centre for Protein Engineering, University of Liège, Institut de Chimie B6, Sart Tilman, 4000 Liège,1 and
2. Fachrichtung 8.8 Biochemie, Universität des Saarlandes, D-66123 Saarbrücken, Germany2;
3. Dipartimento di Biologia Molecolare, Sezione di Microbiologia, Università di Siena, I-53100 Siena, Italy3; and
4. Laboratoire de Biochimie Physique et des Biopolymeres, Université Catholique de Louvain, Bâtiment Lavoisier, 1348 Louvain-la-Neuve,4 Belgium;
5. Department of Chemistry, Wesleyan University, Middletown, Connecticut 064595