Matrix-assisted laser desorption mass spectrometric analysis of a pegylated recombinant protein.

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) has been investigated as a technique for the characterization of recombinant stem cell factor that had been covalently modified with polyethylene glycol (PEG) chains. The attachment of PEG chains produces a heterogeneous mixture of protein species that differ by 6000 Da. These differences in molecular weight could be readily determined by MALDI. The potential of MALDI as a general strategy for characterizing PEG-modified proteins is discussed.