The majority of proteomics applications involve peptide sequencing by liquid chromatography mass spectrometry (LC-MS). Proteins are enzymatically digested to their peptide components, and analyzed by LC-MS. The resulting sequence data is used to determine the original protein components of the sample. Information on posttranslational modifications (PTMs) and stoichiometry can also be obtained with this approach. For single proteins, the sequence can confirm identity and characterize PTMs. For protein complexes this approach determines the identity of the individual proteins that make up the complex, stoichiometry of the subunits and PTMs.