Lysozyme aggregation studied by light scattering .2. Variations of protein concentration

Static and dynamic light scattering have been employed to investigate the behaviour of nucleating lysozyme solutions in the range between 0.34 and 3.08mM. Preselected concentrations of NaCl and (NH4)(2)SO4 have been used to screen the repulsive Coulombic interactions and trigger aggregation. Initially, mass-fractals undergoing diffusion limited-like aggregation coexist with monomers or small lysozyme oligomers. The growth kinetics of the fractals deliver observables that exhibit distinct tendencies when examined as a function of lysozyme concentration. The behaviour of the observables changes drastically around 2.0mM lysozyme. Static light scattering experiments revealed progressive restructuring or growth of compact structures at later stages of the aggregation. Based on the correlations between the observables an attempt is made to predict whether the examined solutions will crystallize or not. A tentative scheme, involving the most prominent structures observed in nucleating lysozyme solutions, is discussed.