1. Institute of Animal Physiology, Department of Veterinary Sciences, LMU Munich, Veterinärstr. 13, D-80539 Munich, Germany, Department of Protein Sciences, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Ingolstaedter Landstr. 1, D-85764 Neuherberg, Germany, and Institute of Human Genetics, Technical University of Munich, Trogerstr. 32, D-81675 Munich, Germany