Relative hydrophobicity of amino acid residues in homooligopeptides as measured by aqueous two-phase partitioning

Partitioning of 17 amino acids and their homooligopeptides of different lengths in an aqueous dextran-PEG two-phase system containing 0.15 M NaCl in 0.01 M sodium phosphate buffer, pH 7.4 and 0.11 M sodium phosphate buffer, pH 7.4 was examined. The relative hydrophobicity of the amino acid residues was estimated and expressed in equivalent numbers of methylene units, Analysis of the data shows that the additivity principle does hold for the hydrophobicity of homooligopeptides. The relative hydrophobicity of essentially all amino acid residues is noticeably affected by the ionic composition of aqueous media.