Solubility enhancement of gluten and organic compounds by arginine

Arginine suppresses protein–protein and protein–surface interactions and thus is expected to increase the solubility of the proteins. We have examined here the effects of arginine on the solubility of a highly insoluble protein, gluten, and two organic compounds, octyl-gallate and coumarin, which have low to moderate aqueous solubilities. Arginine significantly increased the solubility of these molecules concentration dependently, while a weak salting-out salt, NaCl, decreased it. The observed ability of arginine to salt-in these compounds can be explained from its binding to aromatic groups and protein surface. Such solubilizing action of arginine may be used to enhance the solubility of poorly soluble organic drug substances.