Abstract: A method is provided for quantifying a plasma membrane protein present by using a stable-isotope labeled peptide as a probe by mass spectrometry in a simple, quick and accurate manner. A plasma membrane protein is fragmented to prepare an oligopeptide fragment, identified by LC/MS/MS. A subject peptide for quantification is selected if the peptide is obtained by fragmenting with a protease, the peptide is specific to a target molecule, and if the peptide has a high total score value based on selective criteria for hydrophobic amino acids content, sequence conditions, number of amino acid residues, specific amino acid sequence conditions, etc. According to these criteria, a subject peptide fragment that can be ionized by ESI method is selected. By using the subject peptide for and a stable-isotope labeled peptide, the plasma membrane protein is quantified accurately by mass spectrometry.

Abstract: The present invention is to provide a method for quantifying a plasma membrane protein present in a cell membrane, by using a stable-isotope labeled peptide as a probe by mass spectrometry, in a simple, quickly and accurate manner. A plasma membrane protein is fragmented to prepare an oligopeptide fragment, identified by LC-MSMS, and by setting as essential criteria that the peptide is obtained by fragmentizing with a protease, and the peptide is specific to a target molecule, selective criteria with score are set for hydrophobic amino acids content, sequence conditions, number of amino acid residues, specific amino acid sequence conditions, etc. According to criterion for selecting a subject peptide for quantification for selecting preferentially a peptide with high score, a peptide fragment that can be ionized by ESI method is selected, and by using the subject peptide for quantification and a stable-isotope labeled peptide, the plasma membrane protein is quantified accurately by mass spectrometry.