FIGURE 3.

Comparison of PIX rates for apo-UGM (○) versus UGM reconstituted with 5-deaza-FAD (●). Each time course is a plot of the fraction (f) of UDP-Galp possessing ¹⁸O at the bridging C1–OP_β position as determined by ¹³C NMR versus time. As a reference, the PIX rate was ∼100 times faster when UGM was reconstituted with FAD_red. Time courses were determined in separate experiments leading to the difference in the ordinate intercepts (see supplemental data for details). Reactions were run at 27 °C in potassium P_i (pH 7.5), 10% D₂O, and 7 mm Na₂S₂O₄ with 15 μm enzyme. Progress curves were obtained by fitting Equation 1 to the observed time courses using nonlinear regression.