Fig. 6.
EGCG and MEF are partial inhibitors. Reaction progress was monitored at 405 nm. The conditions were as follows: SULT1A1 (1.0 nM, dimer), PAPS (10 μM, 625 × Km), PnP (30 μM, 22 × Km), MgCl2 (5.0 mM), NaPO4 (50 mM), pH 7.2, T = 25 ± 2°C. Less than 5% of the substrate converted at the endpoint of the reaction was consumed during the rate measurements. Each point represents the average of three independent determinations. The lines through the points indicate the behavior predicted by a least-squares fit using a model that assumes a single binding site per subunit. Ki values in the model were fixed using constants in Table 1, and data were fit only for the maximum inhibition value. The best-fit, maximum inhibition values for EGCG and MEF were 88 ± 2 and 94 ± 1%, respectively.