title: Amphiphilicity index of polar amino acids as an aid in the characterization of amino acid preference at membrane-water interfaces.
abstract: BACKGROUND
  An amphiphilicity index of amino acid residues was developed for improving the method of transmembrane helix prediction.
  
  
  RESULTS
  The transfer energy of a hydrocarbon stem group beyond the gamma-carbon was calculated from the accessible surface area, and used to index the amphiphilicity of the residue. Non-zero amphiphilicity index values were obtained for lysine, arginine, histidine, glutamic acid, glutamine, tyrosine and tryptophan. Those residues were found to be abundant in the end regions of transmembrane helices, indicating their preference for the membrane-water interface. The moving average of the amphiphilicity index actually showed significant peaks in the end regions of most transmembrane helices. A dispersion diagram of average amphiphilicity index versus average hydrophobicity index was devised to facilitate discrimination of transmembrane helices.
  
  
  BACKGROUND
  The amphiphilicity index has been incorporated into a system, SOSUI, for the discrimination of membrane proteins and the prdiction of tranmembrane helical regions (http://sosui.proteome.bio.tuat.ac.jp/sosuiframe0.html).
authors.affiliation: Tokyo University of Agriculture and Technology, Faculty of Technology, Department of Biotechnology, Nakacho, Koganei, Tokyo 184-8588, Japan. mitaku@cc.tuat.ac.jp
authors.forename: Shigeki
authors.initials: S
authors.lastname: Mitaku
authors.forename: Takatsugu
authors.initials: T
authors.lastname: Hirokawa
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Tsuji
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry* / Q000145:classification*; D030562:Databases, Protein; D008565:Membrane Proteins / Q000737:chemistry* / Q000145:classification*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D011487:Protein Conformation; D017510:Protein Folding; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014867:Water / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D008565:Membrane Proteins; D014867:Water