Correlation of physicochemical parameters to the hydrophobic contribution constants of amino acid residues in small peptides

Purpose, This paper attempts to correlate the hydrophobic contribution constants (f(aa)) of 21 amino acids in small peptides with commonly used physicochemical parameters. These f(aa) constants can then be used to predict hydrophobicity change in peptides when any one of the amino acid residue is substituted with another. Method, Non-weighted least squares method was used in deriving regression equations with a BMDP program. A Hyperchem program for Windows was used to calculate the group dipole moments of the side chain. Results. A good correlation (r = 0.97) was obtained using a four parameter equation including molecular weight (log MW), hydrogen bond forming ability (HE), dipole moment (mu) and an indicator variable (I) to account for the presence of a free primary amine group in the side chain. Conclusions, This proposed model should be useful in predicting the hydrophobic contribution constants of other uncommon amino acids and in the estimation of log P' values of numerous peptides containing different possible combinations of these amino acids, as well as log P' values resulting from amino acid substitution as is done in site-directed mutagenesis.