DIFFUSIVITY OF PROTEIN IN AQUEOUS-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 super saturated solutions, employing Gouy interferometry. Distilled water, 0 .05 M potassium phosphate buffer, and 0.1 M 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's of the lysozyme solutions in the potas sium phosphate and sodium acetate buffers were adjusted to 6.8 and 4.0 , respectively. The experimental temperature was 25 degrees C. In a sa lt-free system, the concentration dependent diffusion of lysozyme show ed typical electrolyte diffusion behavior, while a salt-polyelectrolyt e system exhibited the behavior of a non-electrolyte. Diffusion result s in the supersaturated region showed a little effect of concentration or solution 'age' at a fixed NaCl concentration. A rapid decline in d iffusion coefficient with increasing NaCl concentration in the supersa turated region, however, was observed.