1. Institute of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Straβe 15, 14163 Berlin, Germany, Institute of Veterinary Biochemistry, Freie Universität Berlin, Oertzenweg 19b, 14163 Berlin, Germany, and Institute of Chemistry and Biochemistry, Biochemistry, Thielallee 63, 14195 Berlin, Germany