1. 1Department of Biochemistry and Chemistry, Royal Free Hospital School of Medicine, (University of London), 8 Hunter Street, London WC1N 1BP, U.K.
2. 2Department of Biochemistry and Chemistry, Royal Free Hospital School of Medicine, (University of London), 8 Hunter Street, London WC1N 1BP, U.K.
3. 3Department of Biochemistry and Chemistry, Royal Free Hospital School of Medicine, (University of London), 8 Hunter Street, London WC1N 1BP, U.K.