An on-line protein digestion device for rapid peptide mapping by electrospray mass spectrometry

A simple laboratory-constructed device has been developed for fast on-line protein digestion followed by peptide mapping by use of electrospray mass spectrometry. Taking advantage of its nonsolubility properties at near-neutral pH values, pepsin could be nonpermanently attached to the PEEK tube commonly employed as transfer capillary between the syringe and the electrospray ion source. After optimization of experimental conditions such as pH, solvent, and exposure time, efficient digestion of several model proteins of molecular weights between 14,000 and 66,000, some having disulfide bridges, was successfully carried out. This technique provided reliable and reproducible sequence information by means of C-terminal-specific cleavages of aromatic and hydrophobic residues. As an application, protein identification could be achieved using a protein database search software.