The effectiveness of three multi-component binding models in describing the binary competitive equilibrium adsorption of two cytochrome b5 mutants

Competitive adsorption isotherms for two conservative surface charge-neutralizing mutants of cytochrome b5, E11Q and E44Q, previously measured with competitor concentration held constant over the range of the isotherm, were used to test three widely-used multi-component isotherm models. The extended Langmuir–Freundlich, Langmuir and Jovanovic–Freundlich models each adequately described the weaker infinite dilution adsorption of the E44Q protein in the presence of the strong binding E11Q. The extended Langmuir–Freundlich model generally gave the lowest errors at higher concentrations, and the Jovanovic–Freundlich model gave the best fits when using empirically optimized maximal loading values based on multi-component as well as pure-component isotherm data.