Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, USA Department of Biochemistry, University of Rochester, Rochester, USA Department of Chemistry, California Institute of Technology, Pasadena, USA Department of Biochemistry, Uniformed Services University Health Sciences, Bethesda, USA Department of Medicine, University of Miami School of Medicine, Miami, USA Institut fur Pharmakologie und Biochemie, Universitit Zurich-Irchel, Zurich, Switzerland ’ Department of Biochemistry, University of California, Berkeley, USA