(A) GC-MS traces of hydrolyzed and derivatized Lan residues from GeoM-modified His6-GeoAII-G−8K (black), His6-GeoAII-S1T (red), dd-Lan standard (blue), dl-Lan standard (pink), and ll- Lan standard (green). (B) GC-MS traces of hydrolyzed and derivatized MeLan residues from GeoM-modified His6GeoAII-S1T (blue), dl-MeLan standard (red), and ll-MeLan standard (black). The small shoulders on the Lan peaks result from partial epimerization during hydrolysis and/or derivatization as previously reported.39 The experiments in panels A and B were conducted with different columns, which led to different retention times.