Quantitative characterization of non-specific interaction of two globular proteins with Dextran T70 in a binary mixture

In a bid to quantify the contribution of molecular structure to non-specific interactions leading to functionally important structural changes in cellular processes, the self-interaction of dextran-T70 (DT70) and its interaction with each of bovine serum albumin (BSA) and ovomucoid trypsin inhibitor (OVO) were studied at pH 7.4 between 5 and 37 °C. The dependences of the apparent molecular weight of each of BSA, OVO and DT70 on the concentration of DT70 were independent of temperature. The activity coefficient of the interaction of each species on DT70 concentration was also independent of temperature. The change in activity coefficient was however dependent on the molecular structure and size of the interacting species. The energy of insertion of each macromolecule in DT70 increased in the order DT70 > BSA > OVO. These findings show that although the enthalpic contribution is negligible, the extent of the entropic contribution to the macromolecular activity coefficient of interaction is chiefly the consequence of the exclusion volume of the interacting macromolecules.