1. Department of Cellular Biochemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany
2. Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
3. Bioanalytics, Institute for Clinical Chemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany