1. Institute of Biochemistry, Swiss Federal Institute of Technology, ETH Centre, Universitätstrasse 16, CH-8092 Zurich, Switzerland, Hospital Ramon y Cajal, Servicio de Bioquimica-Investigacion, CSIC, Ctra. Colmenar Viejo km 9.1, 28034 Madrid, Spain, Department of Internal Medicine, Medizinische Poliklinik, University Hospital, CH-8091 Zurich, Switzerland, and Biochemistry Department, MCP Hahnemann University, 2900 Queen Lane, Philadelphia, Pennsylvania 19129