[1] CENS, DEPT BIOL, F-91191 GIF SUR YVETTE, FRANCE
[2] CENS, DEPT PHYS CHIM, CNRS, LAB 331, F-91191 GIF SUR YVETTE, FRANCE
[3] MUSEUM NATL HIST NAT, BIOPHYS LAB, CNRS, ERA 951, INSERM, U201, F-75231 PARIS 05, FRANCE
[4] CHRISTIE HOSP & HOLT RADIUM INST, PATERSON LAB, MANCHESTER M20 9BX, LANCS, ENGLAND