1. L. Xu and G. Meissner, Departments of Biochemistry and Biophysics, and Physiology, University of North Carolina, Chapel Hill, NC 27599, USA.
2. J. P. Eu and J. S. Stamler, Howard Hughes Medical Institute, Department of Medicine, Divisions of Pulmonary and Cardiovascular Medicine and Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.