1. Department of Chemistry Universität zu Köln Greinstrasse 4 50939 Köln Germany
2. Vth Medical Department Medical Faculty Mannheim University of Heidelberg Theodor-Kutzer-Ufer 1–3 68167 Mannheim Germany
3. Department of Internal Medicine I and Clinical Chemistry University Hospital of Heidelberg 69120 Heidelberg Germany
4. German Center for Diabetes Research (DZD) 85764 Neuherberg Germany