1. Department of Biochemistry, Royal Holloway and Bedford New College, Egham Hill, Egham, Surrey TW20 0EX, U.K.
2. Department of Biochemistry, Scarborough College, West Hill, Ontario, M1C 2C2, Canada
3. Laboratoire de Neurobiologie, L'Hopital de L'enfant Jesus, Quebec, G1J 5B3, Canada