1. Institute of Biochemistry and Molecular Biology, University of Hamburg, Martin-Luther-King Platz 6, 20146 Hamburg, Germany; Institute of Organic Chemistry, Bulgarian Academy of Sciences, “Akad. G. Bonchev”-strasse Bl.9, 1000 Sofia, Bulgaria; Helmholtz-Centre for Environmental Research-UFZ, Department of Proteomics, Permosestrasse 15, 04318 Leipzig, Germany; and Institute of Clinical Chemistry, University Medical Center Hamburg—Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany