Identification of N-terminal modification for recombinant monoclonal antibody light chain using partial reduction and quadrupole time-of-flight mass spectrometry.

Since most recombinant monoclonal antibodies (mAbs) contain glutamic acid or glutamate at their N-terminus, cyclization of these residues to form pyroglutamate is an important degradation pathway that often occurs in therapeutic mAb development. In this work, a rapid method was developed to determine pyroglutamate at the N-terminus of mAb light chain by liquid chromatography coupled with electrospray ionization on a quadrupole time-of-flight mass spectrometer (QTOF). High levels of pyroglutamate were found at the N-terminus of the light chain of a typical recombinant mAb. The quantitative results were comparable to those obtained with a more conventional peptide mapping method. The direct method outlined here can be used to evaluate the impact of N-terminal cyclization during the processing of recombinant mAbs. Copyright 2006 John Wiley & Sons, Ltd.