1. Department of Chemistry, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands.
2. Department of Biochemistry and Biophysics, University of California at San Francisco, San Francisco, CA 94143- 0448.
3. Department of Medical Nutrition and Center for Biotechnology, Karolinska Institute, Huddinge University Hospital, S-141 86 Huddinge, Sweden.