Octamer formation in lysozyme solutions at the initial crystallization stage detected by small-angle neutron scattering.

Solutions of lysozyme in heavy water were studied by small-angle neutron scattering (SANS) at concentrations of 40, 20 and 10 mg ml with and without the addition of precipitant, and at temperatures of 10, 20 and 30°C. In addition to the expected protein monomers, dimeric and octameric species were identified in solutions at the maximum concentration and close to the optimal conditions for crystallization. An optimal temperature for octamer formation was identified and both deviation from this temperature and a reduction in protein concentration led to a significant decrease in the volume fractions of octamers detected. In the absence of precipitant, only monomers and a minor fraction of dimers are present in solution.