DIFFUSIVITY OF LYSOZYME IN UNDERSATURATED, SATURATED AND SUPERSATURATED SOLUTIONS

The diffusion coefficient of lysozyme, a globular protein, was measure d at various conditions as functions of lysozyme concentration, salt c oncentration, and solution ''age'' in concentrated, saturated, and sup ersaturated solutions, employing Gouy interferometry. Distilled water, 0.05M potassium phosphate buffer, and 0.1M sodium acetate buffer solu tions with 0, 2, 4, and 5 wt% NaCl were used as solvents. The pH of ly sozyme solutions in distilled water was 4.75 due to the self-buffering capacity of lysozyme. The pH values of the lysozyme solutions in the potassium phosphate and sodium acetate buffers were adjusted to 6.8 an d 4.0, respectively. The experimental temperature was 25 degrees C. In a salt-free system, the concentration dependent diffusion of lysozyme showed typical electrolyte diffusion behavior, while a salt-polyelect rolyte system exhibited the behavior of a non-electrolyte. Diffusion r esults in the supersaturated region showed little effect of concentrat ion or solution ''age'' at a fixed NaCl concentration. A rapid decline in diffusion coefficient with increasing NaCl concentration in the su persaturated region, however, was observed.