1. Physikalische Biochemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany, Chemistry Department, Glasgow University, Glasgow G12 8QQ, U.K., and Karolinska Institute, Department of Immunology, Microbiology, Pathology and Infectious Diseases, Division of Clinical Bacteriology, Huddinge University Hospital, S-14186 Huddinge, Sweden