1. Eppley Institute and Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805, Unité de Biochimie, Centre de Recherches du Service de Santé des Armées, B.P. 87-38700 La Tronche, France, and United States Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland 21010-5425