1. Scripps Center for Metabolomics and Mass Spectrometry, Scripps Research Institute; La Jolla, California 92037, USA.
2. Department of Molecular Medicine, Scripps Research Institute, La Jolla, CA 92037, USA.
3. Department of Medicine, University of California, La Jolla CA 92093, USA.
4. Department of Structural and Computational Biology, Scripps Research Institute, La Jolla, CA 92037, USA.