Static and Dynamic Light Scattering on Solutions of Precrystalline Β-Galactosidase

A concentration dependent association of β-galactosidase in aqueous buffer solution is demonstrated by static and dynamic light scattering. A procedure is suggested which allows the calculation of the true molar mass of the aggregates from the apparent data measured in a good solvent. The associating system exhibits typical critical behavior with a critical exponent of γ=1.77±0.11 which is characteristic of percolation. The system behaves like a randomly associating ensemble. Evaluation of the curves on the basis of the Flory-Stockmayer (Bethe) theory allowed an estimation of the association number of f=6−7. The measured translational diffusion coefficient is separated in a thermodynamic and a frictional interaction part. Molar mass and friction increase in the same manner up to about a 10% protein solution. Then the friction increases much stronger.