Investigation of the protein pre-crystallization solution using analytical ultracentrifugation

Analytical ultracentrifugation was used to study the crystal growth units in hen egg-white lysozyme pre-crystallization solution. Solutions containing various concentrations of lysozyme and NaCl in 50 mM sodium acetate buffer were used for experiments. The crystallization solution was ultracentrifuged using a mode where the sedimentation and diffusion are in equilibrium. The protein concentration gradient in the centrifugation cell was measured by light absorption and the molecular weight was calculated from the concentration gradient data. The results were analyzed assuming that the molecules have no interaction with each other. In all solutions except for 0.4 M NaCl, 30 mg ml(-1) lysozyme solution, it was shown that the molecular weight falls in the range 12,000-16,500 Da. In 0.4 M NaCl, 30 mg ml(-1) lysozyme solution no analysis was made because crystals appeared at the bottom of the cell after centrifugation. Since the calculated molecular weight of lysozyme monomer is 14,400 Da, it was concluded that the lysozyme molecule predominantly exists as a monomer in undersaturated and supersaturated solutions.