1. Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, Arkansas 72079, Laboratory of Cellular Carcinogenesis and Tumor Promotion, National Cancer Institute, Bethesda, Maryland 20892, Department of Biochemistry, National Institute of Environmental Health, Budapest, H-1097 Hungary, and Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, P-1049-001 Lisboa, Portugal