Fig. S1.
THB inhibition of SULT1A3 is noncompetitive. Reactions were initiated by addition of PAPS at saturation (500 μM, 1,500 × Km), 1-HP concentrations varied from 0.2 to 5 × Km (5–100 nM) in equal increments in double-reciprocal space, and THB concentrations are as indicated. Reaction conditions were as follows: SULT1A1 (10 nM, dimer), KPO4 (50 mM), pH 7.5, 25 ± 2 °C. Reaction progress was monitored by the fluorescence change associated with 1-HP sulfonation (λex 325 nm, λex 370 nm). Less than 5% of 1-HP formed at reaction endpoints was consumed during the measurements. Each point represents the average of two independent determinations. The lines through the points represent the behavior predicted by a global (1/v4)-weighted least-squares fit to a noncompetitive inhibition model. The predicted Ki of THB is 29 ± 3 µM.