Characterization of GntC/GntD/GntG/GntE biosynthetic enzymes with intermediate 2. Relative intensities of positive mode extracted ion chromatograms were extracted from UPLC-MS traces following 1-fluoro-2,4-dinitrophenyl-5-l-alamne amide (l-FDAA; Marfey’s reagent) derivatization of primary amine-containing intermediates 2, 3, 4, 6, and glycine ([M + H]+ (443.16; 425.15; 441.15; 367.15; 328.09) ± 0.20 m/z, respectively) after incubation of 2 with GntC, GntC/GntD or GntC/GntD/GntG/GntE and all necessary cofactors and cosubstrates.