Fig. 2.
Intact protein UPLC–MS data demonstrate Ldt–meropenem adduct lability. (A) Replacement of meropenem on LdtMt2 by faropenem can proceed through three mechanisms: 1) formation of a β-lactone product, 2) hydrolysis of the protein-drug thioester, and/or 3) reclosure of the meropenem β-lactam ring. (B) LdtMt2-meropenem (decarboxylated, 38,425 Da, indicated with one blue circle; intact, 38,469 Da, indicated with two blue circles) was replaced by faropenem (38,172 Da, indicated with three blue circles) after prolonged incubation.