1. Molecular Biology Division, Department of Veterans Affairs Medical Center, San Francisco, CA 94121 and Department of Biochemistry and Biophysics and the Department of Anesthesia, University of California, San Francisco, CA 94143.
2. Department of Chemistry, University of California, Berkeley, CA 94720.
3. W. M. Keck Laboratories, California Institute of Technology, Pasadena, CA 91125.