A rapid method for the identification and characterization of proteins in bacterial cell-free extracts has been developed using directly combined liquid chromatography-electrospray mass spectrometry. The usefulness of this technique is demonstrated for monitoring the expression and chemical modification 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 resolution, reproducibility and the ability, unlike gel electrophoresis, to directly identify post-translational modifications. The advantages of this technique over analogous matrix-assisted laser desorption ionization mass spectrometry approaches and its potential as a standard tool in the biomolecular research laboratory are discussed.
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