1. Contribution from the Department of Chemistry, University of Southern California, Los Angeles, California 90089, Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, Institut für Klinische Chemie und Pathobiochemie, Institut für Biochemie, Universität Leipzig, 04103 Leipzig, Germany, Departments of Molecular Pharmacology and Biochemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461