(41d) Correlation of Protein–Protein Cross Interactions with Separations Behavior

Protein-protein interactions, whether desirable or not, can have a direct effect on performance measures of protein separations. The most obvious of these are interactions between like molecules, which determine the thermodynamic properties and phase behavior of protein solutions. However, interactions between unlike molecules affect the properties of protein mixtures, which are present by definition in protein separations. Here we seek to quantify these effects by comparing direct measurements of protein-protein cross interactions with measures of separations performance in various processes. The cross-interactions are measured by cross-interaction chromatography, a variant of affinity chromatography that provides data that can be expressed in terms of the virial cross-coefficient. We review our earlier results for ultrafiltration, where the effect of BSA on lysozyme filtration is shown to be correlated with BSA?lysozyme cross-interactions. Self- and cross-interaction measurements are also used to explain performance of two other types of separations. First, they are used to help optimize the use of selective precipitation to separate lysozyme and ovalbumin. Second, they explain some anomalous trends seen in adsorption isotherms for binary mixtures of lysozyme, cytochrome c and ribonuclease A on cation-exchange resins. These results, taken together, show that the complexity of protein interactions can explain anomalies and inconsistencies that frequently confound the extraction of meaningful general trends in separations analyses.