KINETICS OF LOW PH INDUCED AGGREGATION OF EQUINE IGG

The kinetics of soluble aggregate formation in equine IgG was studied in the pH 3.4-4.3 range and ionic strength between 0.02 and 0.5 M, and a diagram describing aggregation kinetics as diffusion limited, react ion limited, or transitional as a function of pH and ionic strength wa s constructed. Aggregation rate is limited by the degree of electrosta tic repulsion between the protein molecules in the pH 4.0-4.5 range. B elow pH 4.0, a greater degree of attractive force is present, most lik ely from protein unfolding, and electrostatic repulsion no longer dete rmines the rate of aggregation. The aggregation rate increases with de creasing pH, and at pH 3.4 the aggregation rate is diffusion limited. The pH range separating reaction-limited and diffusion-limited kinetic s decreases with increasing ionic strength, indicating charge shieldin g from the buffer solution influences the aggregation rate. (C) 1997 A cademic Press.