FIGURE 5.

QSOX cooperates with PDI to refold RfBP. Avian QSOX (0–500 nM) in 50 mM phosphate buffer (pH 7.5, 1 mM EDTA, 25 °C), was mixed with 0.8 μM riboflavin and 30 μM reduced human PDI (120 μM CxxC thiols; see Experimental Procedures). The reaction was initiated by the addition of reduced RfBP (1 μM; 18 μM cysteine thiols with a carry-over of ~ 50 mM guanidine hydrochloride). Binding of riboflavin was assessed by the decrease in riboflavin fluorescence emission.