Peptide hydrophobicity and partitioning in poly(ethylene glycol)/magnesium sulfate aqueous two-phase systems.

Several amino acids and peptides were partitioned in poly(ethylene glycol) (PEG)/magnesium sulfate (MgSO4) aqueous two-phase systems. The partition coefficients measured for amino acids and peptides were proportional to the difference in PEG concentration between the phases. The partitioning data were used to calculate the relative hydrophobicities of individual amino acids, which were then used to estimate the hydrophobicities of peptides. The partition coefficients of several dipeptides were predicted from these estimated hydrophobicities. A series of peptide fragments that compose the pentapeptide leucine enkephalin was also partitioned in the PEG/MgSO4 system. Again, the partitioning depended upon the hydrophobicities of the individual exposed amino acids.