1. Department of Chemistry, University of Leicester, Leicester LE1 7RH, U.K.
2. School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.
3. Protein and Nucleic Acid Laboratory, University of Leicester, Leicester LE1 7RH, U.K.
4. Department of Cell Physiology and Pharmacology, School of Medical Sciences, University of Leicester, Leicester, LE1 9HN, U.K.