1. Department of Physiological Chemistry at Karolinska Institutet, S-104 01 Stockholm, Sweden.
2. Department of Physiology at Karolinska Institutet, S-104 01 Stockholm, Sweden.
3. Department of Pharmacology at Merck Frosst Canada, Pointe-Claire-Dorval, Quebec HF9R 4P8, Canada.
4. Hematology Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, U.S.A.