FIG. 4.

Flavin binding to StyA1 and StyA2B. (a) Purified StyA1 and StyA2B were tested for noncovalently bound flavins by RP-HPLC as described in Materials and Methods. Bovine serum albumin (BSA) was used as a blank, and a multipoint calibration for each flavin standard allowed flavin determination up to a low μM range. (b) Normalized fluorescence emission (F/F₀) from tryptophans of StyA1 (0.59 μM; +) or StyA2B (0.66 μM; •) measured at 340 nm (excitation 290 nm) during flavin titration with FAD to estimate dissociation constants of apoenzyme-flavin complexes.