1. Laboratory of Proteomics and Analytical Technologies, SAIC−Frederick, Inc., National Cancer Institute at Frederick, P.O. Box B, Frederick, Maryland 21702-1201, Toxinology Division, Department of Immunology and Molecular Biology, U.S. Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, 21702-5011, and Anaerobic Bacteria and Toxins Unit, Institut Pasteur, 28 rue Docteur Roux, Paris, 75724 France