Effect of the relative concentrations of ATP and MgCl
on PAPS synthesis. Na2SO4 (26 μM containing 10 μCi of labeled sulfate) was incubated at 37°C in 100 mM Tris-HCl buffer pH 8.5, 5 mM GTP (A) at different ratios of [ATP]/[Mg2+]. Each bar corresponds to the mean of 2 to 4 experiments, performed at different ATP and Mg2+ concentrations while keeping the same ratio. (B) at a ratio value of 1, at either 5 mM MgCl2, 5 mM ATP (▲) or 20 mM MgCl2, 20 mM ATP (●).