1. Departments of Biochemistry and Chemistry, Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, Institute of Environmental Medicine, Division of Biochemical Toxicology, Karolinska Institutet, SE-17177 Stockholm, Sweden, and Department of Biosciences and Nutrition, Karolinska Institutet, and School of Technology and Health, Royal Institute of Technology, SE-14157 Huddinge, Sweden