Abstract: A new method to identify allergen of Periplaneta americana with HPLC-ESI-MS/MS was established.  The protein with molecular weight of 74 kD from
P. americana was purified by sequential chromatography of two steps including ion exchange chromatography and gel filtration chromatography. After ingel digestion of allergen,the tryptic peptide mapping of allergen was obtained by HPLC-ESI-MS/MS. The data were then searched against NCBInr database using MS/MS Ions search (http://www.matrixscience.com). We compared the results of identification of 74 kD protein from the crude extract of P. americana and  from  the purified protein to evaluate the effect of purification. Our data showed that the purified protein with molecular weight of 74 kD is the major allergen of P. americana. The steps of chromatography are effective to remove the other protein with the same size as the purified protein. To our knowledge， this is the first report on the identification of the major allergen from P. americana by HPLC-ESI-MS/MS. The research indicated that the MS is simple and universal for the quality control of naturally purified allergen.   

Key words: Periplaneta americana, liquid chromatography, electrospray ionization trap, tandem mass spectrometry, allergen, identification