1. L. Shu and L. Que Jr., Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA.
2. J. C. Nesheim and J. D. Lipscomb, Department of Biochemistry, Medical School, and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, MN 55455, USA.
3. K. Kauffmann and E. Münck, Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.