The influence of radioiodination on the adsorption of IgG and serum albumin to polystyrene

The adsorption of radioiodinated rabbit IgG and bovine serum albumin (BSA) to polystyrene tubes was investigated. Adsorption isotherms where the proportion of the protein bound was relatively constant over a range of intermediate protein concentrations, and where the proportion bound was protein dependent, were obtained. To investigate the effects of radioiodination, proteins labeled to give a wide range of substitution ratios (0.03 to 3.7 ¹²⁵I/protein molecule) were employed. While labeling did not appear to affect BSA adsorption, the kinetics of IgG binding were altered in a number of ways. The proportion bound in the concentration independent region was decreased even at substitution ratios ≤0.2. In addition, while all preparations of iodinated BSA, and IgG preparations with ≤1.6 ¹²⁵I IgG, gave bimodal adsorption isotherms, with more heavily labeled IgG (≥2.5 ¹²⁵I IgG) the apparent high afinity binding to the plastic surface was abolished. These results indicate that radioiodination substantially alters the kinetics of the binding of IgG to polystyrene. In addition, the results obtained are discussed with respect to previous relevant and often apparently contradictory findings.