1. Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, Department of Chemistry, York College, City University of New York, 94-20 Guy R. Brewer Boulevard, Jamaica, New York 11451, Department of Biochemistry & Molecular Biology, University of Texas Medical Branch, 5.154 Medical Research Building, Galveston, Texas 77555-1052