Amino Acid Solubility and Protein Stability in Aqueous Maltitol Solutions

Abstract

The solubilities of several amino acids and diglycine were measured in aqueous maltitol solutions at 25°C to evaluate the free energy of transfer of amino acid side-chains and peptide groups from water to aqueous maltitol solutions. The free energy of transfer was positive for most nonpolar side-chains, oppositely negative for most polar side-chains, and zero for the peptide group. The corresponding enthalpies and entropies of transfer, which were measured calorimetrically, were positive for nonpolar side-chains and negative for the peptide group. These results suggest that as well as other polyols and sugars, maltitol could stabilize protein structures through strengthening of the hydrophobic interaction. The thermal stability of a model protein, ribonuclease A, increased with increasing concentrations of maltitol, its stabilizing ability being comparable with maltose but less than glucose and sorbitol.