Direct MS/MS analysis of proteins blotted on membranes by a matrix-assisted laser desorption/ionization-quadrupole ion trap-time-of-flight tandem mass spectrometer.

We constructed a system for the microscale identification of membrane-blotted proteins by proteolytic digestion using an instrument developed with piezoelectric chemical inkjet technology and MS/MS analyses of the resulting peptides with a matrix-assisted laser desorption/ionization-quadrupole ion trap-time-of-flight tandem mass spectrometer (MALDI-QIT-TOF MS). Using this system, bovine serum albumin was clearly identified at levels less than 100 fmol, and proteins from an Escherichia coli extract were also identified by an MS/MS ion search.