Parallel quantification method of protein variants

Action in vivo by variants different proteins there are many. To more accurately determine the effect of protein in vivo, when quantifying the proteins in the sample, it is required to determine the amount of each mutant that may be present, respectively. A method of quantifying in parallel each mutant protein having 2 or more variant by mass spectrometry, the protein in the sample to protease digestion, among peptide obtained by the protease digestion, unique to each mutant a peptide having an amino acid sequence was detected by without mass spectrometry separating comprises determining the amount of each variant in a sample based on the result, to provide the method.