(A) Detection (left panel) and quantification (right panel) of steady-state conversion of endogenous MgtE by YqgP (strain BS72, Table EV2) grown in minimal M9 medium containing 10 μM MgSO4 and 1 μM each of MnCl2, ZnCl2, CoCl2, NiCl2 and CaCl2 (reference conditions) with the additions of 10 µM or 100 μM of a given divalent cation salt solution (MnCl2, ZnCl2, CoCl2, or NiCl2), or 50 µM and 500 μM for CaCl2. Western blots were quantified by near-infrared fluorescence detection (left), quantified by densitometry and displayed as relative specific activity (graph on the right), which is substrate conversion normalized to enzyme expression level. Black arrow denotes full-length substrate (MgtE), and red arrow denotes the N-terminal cleavage product(s) generated by YqgP. All bands originate from the same western blot and identical treatment series. 