How to manipulate partition behavior of proteins in aqueous two-phase systems: Effect of trimethylamine N-oxide (TMAO)

Abstract

It is shown that the partition behavior of solutes in a given aqueous two-phase systems can be manipulated using a nonionic additive, the trimethylamine N-oxide (TMAO). To this end, partitioning of a set of proteins and small organic compounds was analyzed in aqueous Dextran-75-Polyethylene glycol (PEG-600)-0.15 M sodium sulfate-0.01 M sodium/potassium phosphate buffer, pH 7.4 two-phase systems with TMAO additive at different concentrations from 0 up to 1.95 M. Partition behavior of several proteins was also examined in aqueous Ficoll-70-Polyethylene glycol (PEG-8000)-0.01 M sodium/potassium phosphate buffer, pH 7.4 two-phase systems with TMAO additive at different concentrations in a range from 0 up to 1.5 M. It has been found that protein partitioning changes with the increasing TMAO concentration in the protein specific manner. The differences between the solvent properties of water in the phases of the aqueous two-phase systems, such as hydrophobic character, electrostatic properties, solvent dipolarity/polarizability, hydrogen bonding donor acidity, and hydrogen bonding acceptor basicity were characterized with (a) analysis of partitioning of homologous series of sodium salts of dinitrophenylated amino acids with aliphatic alkyl side-chains, and (b) solvatochromic comparison method. The results obtained show that TMAO affects partitioning of solutes via its effect on the solvent properties of the phases, in agreement with the view that partition behavior of proteins and small organic compounds is governed by the solute-water interactions in the coexisting phases.