1. Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
2. Department of Chemistry, Georgetown University, Box 571227, Washington, D.C. 20057, United States
3. Laboratory of Applied Mass Spectrometry, National Heart, Lung & Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
4. NIH Chemical Genomics Center, NIH Center for Translational Therapeutics, National Institutes of Health, 9800 Medical Center Drive, MSC 3370, Bethesda, Maryland 20892, United States