a, PAGE results. As in Fig. 3, the upper band is the unreacted PC complex, the middle band is excess P and the bottom band is the product XC or SC band. b, High discrimination factors were observed for all conditions tested (see Supplementary Figs S12–S14 for more details and results quantitation), with median Q = 34 across conditions. The histogram includes data from Fig. 3b, where the X1 7/5 probe was operated at standard conditions of 25 °C, 11.5 mM Mg2+ and 100 nM PC.