FIGURE 2.

Redox titration of SQR-bound FAD. The titration was performed as described under “Experimental Procedures” in the presence of indigo carmine as a reference dye. Top panel, FAD reduction was monitored at 465 nm (the isosbestic point for the reference dye), and the reduction of the dye was followed at 640 nm. Bottom panel, Nernst-plot analysis of the estimated standard reduction potential of the solution versus the fraction of oxidized SQR-bound FAD. The spectrum (top) is representative of three independent experiments, whereas the lower panel shows data from all three experiments. NHE, normal hydrogen electrode; ox/red, oxidized/reduced.