1. Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands, Institute for Veterinary Research, IVW/GSAH, PO Box 80163, 3508 TD Utrecht, The Netherlands, and Department Biochemistry and Cell Biology, Faculty of Veterinary Medicine and Institute of Biomembranes, Utrecht University, PO Box 80176, 3508 TD Utrecht, The Netherlands