J. Biol. Chem., Vol. 261, Issue 16, 7220-7222, Jun, 1986
The role of solvent polarity in the free energy of transfer of amino acid side chains from water to organic solvents
S Damodaran and KB Song
The transfer free energies of amino acid side chains from water to N-
methylacetamide have been determined and compared with those obtained from
other model systems. Although the process of transfer from water to
N-methylacetamide represents transfer from a lower dielectric phase to a
higher dielectric phase, the transfer free energies of most of the amino
acid side chains are nearly the same as those obtained from the water to
ethanol system. Among the apolar side chains studied, only the transfer
free energies of methionine and the aromatic side chains are apparently
influenced to some extent by the polarity of the organic solvent phase. The
transfer free energies of the neutral polar side chains also exhibit
significant dependence on solvent polarity. The van't Hoff plots for most
of the apolar side chains exhibit nonlinear curves, indicating that the
enthalpy of transfer from water to N- methylacetamide is
temperature-dependent. It is suggested that to assess the contribution of
the hydrophobic free energy to the stability of globular proteins, it is
probably not necessary to account for variation in the internal environment
of the protein.