1. Department of Biology, University of Maryland, College Park, MD 20742, U.S.A.
2. Department of Pharmaceutical and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29403, U.S.A.
3. Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29403, U.S.A.
4. Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing, NY 11367, U.S.A.