Apparent molecular mass of proteins eluted from gel filtration columns was deduced from a calibration carried out with LMW and HMW calibration kits (Amersham Pharmacia Biotech). The theoretical Stokes radii (R S ) of a native (R S N) and fully unfolded (R S U) protein with a MM (in Daltons) were calculated according to (Uversky 1993) : log(R S N) = 0.369 Á log(MM) À 0.254 and log(R S U) = 0.533 Á log(MM) À 0.682.