Size exclusion chromatography on Superdex-200 of apo-, holo- and reconstituted StyAs. Left Samples of 100 µL protein (1.95 mg mL−1 StyA1, 2.17 mg mL−1 StyA2B, 11.45 mg mL−1 StyA) were loaded onto the column. Elution was performed in 10 mM Tris–HCl (pH 7.2), 500 mM sodium chloride, pH 7.2 at 22°C. The flow rate was 0.6 mL min−1. Reconstituted enzymes were prepared by incubating both protein and buffer with 12.7 µM FAD, either in the absence or presence of 1 mM sodium dithionite. Right Distribution of the isoforms in the three conditions: apo, holo and reduced StyA. Intensity of arrows shows dominant direction of equilibrium (compare with Table 3).