FIGURE 2.

YUC6 contains FAD as a cofactor. A, UV-visible spectrum of YUC6, which has absorbance peaks at 448 nm and 376 nm. The inset is a SDS-polyacrylamide image indicating that YUC6 was purified to near homogeneity. B, fluorescence excitation spectra of YUC6 before and after various treatments. Emission was recorded at 525 nm. The black fluorescence spectrum is of the as-isolated His-tagged YUC6. Treatment with 0.1% SDS causes a slight increase in fluorescence (blue spectrum). Phosphodiesterase treatment of denatured (SDS-treated) YUC6 yields the red spectrum, which exhibits a large increase of fluorescence, indicating that the native flavin cofactor is FAD.