Primary Structure Details of Haptoglobin α Chain Proteins from Human Plasma Samples are Resolved by Matrix-Assisted Laser Desorption/Ionization Quadrupole Ion Trap Time-of-Flight Multiple-Stage Tandem Mass Spectrometry Sequencing

Abstract

Matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight multiple-stage tandem mass spectrometry analyses lead to the rapid identification of protein structural details, as readily interpretable spectra after peptide fragmentations were obtained showing ion signals with high abundance even with sample amounts in the low femtomole range. In our studies we show that the Hpα1F form that contained a C-terminal arginine residue was found to be the only contributing component to spot 149. By contrast, spots 77 and 79 were found to consist of two haptoglobin forms each. Spot 77 consists of Hpα1S and deamidated Hpα1F, whereas spot 79 consists of Hpα1F and of Hpα1S that contains a C-terminal arginine residue. The use of ion traps, enabling the acquisition of MS n spectra serves as a powerful peptide sequencing method for the analysis of both genetic differences and post-translational modification events as the main reason for the observed spot pattern in the 2-D gels of haptoglobin proteins.