TY - JOUR T1 - Measurement and Correlation of Partition Coefficients of Polar Amino Acids JF - Molecular Pharmacology JO - Mol Pharmacol SP - 602 LP - 608 VL - 20 IS - 3 AU - LIBBY M. YUNGER AU - RICHARD D. CRAMER III Y1 - 1981/11/01 UR - http://molpharm.aspetjournals.org/content/20/3/602.abstract N2 - The distribution coefficients of 12 commonly occurring amino acids were measured with high precision by a radiometric method. Values obtained for the logarithm of the ratio of distribution between octanol and 10 mM phosphate buffer, pH 7.0, are as follows: tryptophan, -1.11; histidine, -1.95; valine, -2.26; proline, -2.54; 3-carboxypiperidine, -2.66; alanine, -2.74; threonine, -2.94; serine, -3.07; γ-aminobutyric acid, -3.17; lysine, -3.05; glutamic acid, -3.69; and arginine, -4.08. Preliminary studies at other pH values show that, at pH 7, the charged amino acids partition into the octanol phase in their charged form. These and literature results can be reconciled with partition coefficient additivity rules most easily by assuming that (a) structural changes affect amino acid partitioning by only 0.6 of their effect on more lipophilic molecules, and (b) in octanol the NH3+ and COO- moieties "self-solvate" polar side-chains as well as each other. The experimental values for the partition coefficients correlate moderately well with the hydrophobicity scale of Nozaki and Tanford [J. Biol. Chem. 246:2211-2217 (1971)]. ACKNOWLEDGMENT We thank Dr. W. Bondinell for a valuable experimental suggestion. ER -