Large molecule quantification by LC–MS
To date, almost all protein LC-MS/MS based bioanalysis has involved the use of trypsin to cleave biopharmaceuticals into manageable peptides for quantitation. In some cases, where trypsin does not generate useful peptide sequences, a different cleavage agent is required. Glu-C is an enzyme that is frequently used for protein characterisation, and cuts proteins on the C-terminal side of the aspartic and glutamic acid residues. These two molecules are acidic amino acids, whereas the ubiquitous trypsin cleaves at the basic residues (lysine and arginine), therefore making this an orthogonal cleavage enzyme.