1. Institute of Biochemistry, University Clinics Charité, Humboldt University, Hessische Strasse 3-4, 10115 Berlin
2. Department of Internal Medicine, Universitätsklinikum Benjamin Franklin, Free University Berlin, Hindenburg Damm 30, 12200 Berlin
3. Clinic for Internal Medicine, Division of Endocrinology and Metabolism, University of Heidelberg, Bergheimer Strasse 58, 69115 Heidelberg, Federal Republic of Germany