Proteomics using digestion of proteins followed by analysis by mass spectrometry has found wide acceptance as a way to investigate cellular expression and control. The most common protease used for digestion of proteins to produce peptides in simple or complex mixtures is Trypsin (NEB #P8101). Trypsin is treated with TPCK to destroy chymotryptic activity and acetylated on Lysine residues to prevent autolysis. Trypsin digestion produces peptides that have two positive charges in acidic solutions: the N-terminal amino group and at the C-terminal of Lysine or Arginine on the side chain. These doubly charged peptides are fragmented by Collision-Induced Disassociation (CID) and produce fingerprint spectra in a tandem mass spectrometer. A program such as Sequest or Mascot is then used to compare these spectra to the in silico predicted spectra to find the best matches if any.
Other proteases such as the Endoproteinases GluC (NEB #P8100), AspN (NEB #P8104), LysC and ArgC are also used to generate peptides that can be used in the same way. These other specificities can be used to generate larger peptides with more charges per peptide or to isolate a specific peptide when looking for a specific modification.
Trypsin-digested BSA MS Standard (CAM-modified) (NEB #P8108) is a complex mixture of peptides produced by Trypsin digestion of Bovine Serum Albumin (BSA) that was reduced and alkylated with Iodoacetamide (CAM-modified). This peptide mixture can be used to test a Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI-TOF), test a chromatographic separation or Electrospray Ionization (ESI) mass spectrometer (TOF, Q-TOF or Ion Trap).