Characterization of large, heterogeneous proteins by electrospray ionization-mass spectrometry.

Characterization of heterogeneous proteins as large as 150,000 u was performed by a quadrupole mass spectrometer by using electrospray ionization (ESI). We were able to determine not only the molecular weight, but the detailed heterogeneity for the large glycoproteins as well. The successful application was facilitated by the optimization of the instrument in the high mass-to-charge range up to m/z 4000, where the multiply charged envelopes of the 150,000-u glycoproteins were found. For the analysis of clinically important monoclonal antibodies mass spectral data acquired by this method were consistent with the carbohydrate analysis and were useful in resolving the monosaccharide data into glycoform variations. In the case of the characterization of other large, heterogeneous proteins such as elongation factor 3 and bovine serum albumin, the quadrupole ESI mass spectrometer provided adequate mass resolution and high mass measurement accuracy to discern the modification and degradation of the proteins.