Observation of precrystallization aggregation in protein solutions during centrifugation

Sedimentation velocity experiments on supersaturated solutions of either lysozyme or papain were performed to analyse the nucleation process as a prerequisite for crystal growth. The method is based on the determination of oligomers from sedimentation patterns, the calculation of equilibrium constants for the association reactions and the estimation of the free energy involved in such processes. The transition from the state of unfavourable free energy that is necessary for the formation of smaller oligomers to that of free energy released in larger systems ensues in assemblies of fifteen to twenty molecules for both proteins. The observation of nuclei in less than one hour permits this method to be used for early recognition of crystal growth.