Rigid structure of fractal aggregates of lysozyme

The aggregation of hen egg-white lysozyme upon salt addition was studied by quasi-elastic light scattering. Our results agree with the fractal structu re of the aggregates already reported in the literature. However, we also d emonstrate that these aggregates are rigid, since they do not display any f luctuation of internal concentration. Such a rigid internal structure is a key point to reconcile the fractal structure of the aggregates and their co lloid-like ordering. Furthermore, this result has to be considered for unde rstanding crystal nucleation.