1. Department of Medicine Laboratories, Bristol Royal Infirmary, Bristol BS2 8HW, U.K.
2. Department of Pathology and Microbiology, School of Medical Sciences, Bristol BS8 1TD, U.K.
3. Biochemistry Department, Hospital for Sick Children, Toronto M5G IX8, Canada
4. Biochemisches Institut II, Universität Kiel, D-24098 Kiel, Germany