1. Department of Biology, Northeastern University, Boston, Massachusetts 02115, ValiGene, Paris 92086, France, Sphinx Pharmaceuticals, A Division of Eli Lilly and Co., Cambridge, Massachusetts 02139, Laboratory for Mass Spectrometry and Gaseous Ion Chemistry, Rockefeller University, New York, New York 10021, Department of Chemical Engineering, Northeastern University, Boston, Massachusetts 02115, and Department of Laboratory Medicine, Children's Hospital, Boston, Massachusetts 02115