1. Laboratory for Biological and Medical Mass Spectrometry, Uppsala University, Box 583 Biomedicum, SE−75123, Sweden, Mass Spectrometry Research Center, Vanderbilt University School of Medicine, 465 21 Avenue South, Room 9160 C, Nashville, Tennessee 37232-8575, and Department of Physiology and Pharmacology, Karolinska Institute, SE−17177 Stockholm, Sweden