1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
2. Centre
for Molecular and Structural Biochemistry, School of Chemistry, and
School of Biological Sciences, University of East Anglia, Norwich
Research Park, Norwich NR4 7TJ, United Kingdom