  We investigate the solvent-accessible area method by means of Metropolis
simulations of the brain peptide Met-Enkephalin at 300$ K$. For the energy
function ECEPP/2 nine atomic solvation parameter (ASP) sets are studied. The
simulations are compared with one another, with simulations with a distance
dependent electrostatic permittivity $\epsilon (r)$, and with vacuum
simulations ($\epsilon =2$). Parallel tempering and the biased Metropolis
techniques RM$_1$ are employed and their performance is evaluated. The measured
observables include energy and dihedral probability densities (pds), integrated
autocorrelation times, and acceptance rates. Two of the ASP sets turn out to be
unsuitable for these simulations. For all other systems selected configurations
are minimized in search of the global energy minima, which are found for the
vacuum and the $\epsilon(r)$ system, but for none of the ASP models. Other
observables show a remarkable dependence on the ASPs. In particular, we find
three ASP sets for which the autocorrelations at 300$ $K are considerably
smaller than for vacuum simulations.
