Human Metabolism Section, Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina (S.-Y.Z., S.S., S.C., J.A.G.); and CellzDirect/Invitrogen Corp., Durham, North Carolina (S.S.F.)

Human Metabolism Section, Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina (S.-Y.Z., S.S., S.C., J.A.G.); and CellzDirect/Invitrogen Corp., Durham, North Carolina (S.S.F.)

Human Metabolism Section, Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina (S.-Y.Z., S.S., S.C., J.A.G.); and CellzDirect/Invitrogen Corp., Durham, North Carolina (S.S.F.)

Human Metabolism Section, Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina (S.-Y.Z., S.S., S.C., J.A.G.); and CellzDirect/Invitrogen Corp., Durham, North Carolina (S.S.F.)

Human Metabolism Section, Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina (S.-Y.Z., S.S., S.C., J.A.G.); and CellzDirect/Invitrogen Corp., Durham, North Carolina (S.S.F.)