1. 1Courtauld Institute of Biochemistry, The Middlesex Hospital Medical School, London W1P 7PN, U.K.
2. 2Courtauld Institute of Biochemistry, The Middlesex Hospital Medical School, London W1P 7PN, U.K.
3. 3Courtauld Institute of Biochemistry, The Middlesex Hospital Medical School, London W1P 7PN, U.K.