Identification of proteins in cell-free extracts using liquid chromatography-electrospray ionization mass spectrometry

A rapid method for the identification and characterization of proteins in b acterial cell-free extracts has been developed using directly combined liqu id chromatography-electrospray mass spectrometry. The usefulness of this te chnique is demonstrated Sor monitoring the expression and chemical modifica tion of phosphoenolpyruvate-sugar phosphotransferase system (PTS) proteins from E. coli with molecular masses ranging from 9-65 kDa. The technique is characterized by minimal sample preparation, remarkable mass accuracy and r esolution, reproducibility and the ability, unlike gel electrophoresis, to directly identify posttranslational modifications. The advantages of this t echnique over analogous matrix-assisted laser desorption ionization mass sp ectrometry approaches and its potential as a standard tool in the biomolecu lar research laboratory are discussed.