1. Department of Medical Biochemistry and Microbiology, Uppsala Biomedical Center; Uppsala University; 751 23 Uppsala Sweden
2. Laboratory of Physical Chemistry; Swiss Federal Institute of Technology, ETH-Hönggerberg; Vladimir-Prelog-Weg 28093 Zürich Switzerland
3. Department of Biochemistry and Molecular Genetics; University of Colorado at Denver; 12801 East 17th Avenue Aurora CO 80045 USA