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 1A4, Canada
3. Laboratoire de Neurobiologie, L'Hopital de L'enfant Jesus, Quebec, G1J 5B3, Canada