The apolar surface area of amino acids and its empirical correlation with hydrophobic free energy.

A linear equation is presented which accounts quantitatively for the free energy of transfer of amino acids from water to apolar solvent as a function of accessible surface area and partial charges of the constituents of amino acids. Starting from these parameters the apolar surface area is defined and correlated with the measured free transfer energy. The resulting linear correlation makes it possible to calculate more precisely the "hydrophobic" contribution of both apolar and polar groups including uncharged side chains of arginine, lysine, glutamic and aspartic acids, and histidine, respectively, to protein stabilization.