1. Department of Biochemistry, The Hebrew University of Jerusalem, Hadassah School of Medicine, 91120 Jerusalem, Israel
2. Laboratoire de Biochimie, Faculte de Medecine, St. Antoine, 27 rue de Chaligny, 75571 Paris 12, France
3. Laboratoire de Physico‐Chimie de l 'Adaptation Biologique (INSERM U 312), Museum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris 05
4. Department of Radiation Oncology, Fox Chase Cancer Center, 7701 Burholme Avenue, Philadelphia PA 19111, USA