Hydrophobic interactions

Hydropathy index is a measure used in the field of biochemistry to determine the hydrophobicity or hydrophilicity of amino acids. The index was first introduced by Jack Kyte and Russell F. Doolittle in 1982. It has been instrumental in understanding protein structure and protein-protein interactions.

Overview

The hydropathy index of an amino acid is defined as the free energy change of transferring it from its standard state in water to a reference state in 1-octanol. The index ranges from -4.5 to 4.5, with negative values indicating hydrophilic residues and positive values indicating hydrophobic residues.

Calculation

The hydropathy index is calculated based on the partitioning of amino acids between water and the nonpolar phase of a two-phase liquid system. The index is derived from the logarithm of the partition coefficient, which is the ratio of the concentrations of the amino acid in the two phases at equilibrium.

Applications

The hydropathy index is used in various applications in biochemistry and molecular biology. It is used to predict the secondary structure of proteins, to identify potential transmembrane proteins, and to study protein-protein and protein-lipid interactions.

See also

• Hydrophobic effect
• Partition coefficient
• Protein structure
• Transmembrane protein