1. Contribution from the Department of Chemistry and Laboratory for Biochemical and Genetic Engineering MS-60, William Marsh Rice University, 6100 Main Street, Houston, Texas 77005-1892, the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, the Center for Metalloenzyme Studies, University of Georgia, Athens, Georgia 30602-2556, and the Department of Chemistry, Auburn University, Auburn, Alabama 36849