Associative interactions between pullulan and negatively charged bovine serum albumin in physiological saline solutions

Abstract

In the present study, the behavior of bovine serum albumin (BSA) and pullulan (PULL) mixtures was investigated in physiological saline solution at 37 °C and pH = 7.4 (above the isoelectric point of BSA), by viscometry and membrane osmometry. The new Wolf approach was used for modeling the viscometric behavior of the PULL/BSA saline solutions. From the viscometric data, the contributions of binary, ternary and quaternary intersegmental contacts were determined. Osmotic pressure measurements were carried out as a function of PULL/BSA mixture concentration and composition. In dilute 0.15 M NaCl solutions, the electrostatic repulsion between the BSA molecules is partially screened and attractive PULL/protein interactions are mediated by Na ions. Thus, large deviations from ideal behavior were observed for BSA containing systems. This effect could be attributed to complexes formation as the protein content increases in the solution. The complexation was depicted as the adsorption protein molecules on the PULL chains through the electrolyte molecules. The results obtained by viscometry and osmometry were corroborated, allowing the prediction of the phase behavior of the mixtures. The reported experimental results provide useful information for the design of new biomaterials starting from pullulan and globular proteins.

Keywords: Bovine serum albumin; Intermolecular interactions; Mixed coil; Osmotic pressure; Pullulan; Viscosity.