The protein-binding isotherms exhibit a multiple sigmoi- dal shape with an onset that occurs at a lower concentration for the MIPs than the NIPs; the MIPs retain considerably more protein at the saturation level (Figure 3). This result precludes curve fitting to any of the common adsorption models. PIgG shows at least two sigmoidal steps, with the first step occurring between 0.05 and 0.15 mg mL