Native ATP sulfurylase. Isolated from Baker's Yeast. A key enzyme in the activation of inorganic sulfate required for enzymatic sulfation. Useful for the synthesis of PAPS. Recommended reaction conditions: 50 mM Tris-HCl, 20 mM MgCl2, pH 8.0. Specific Activity: 5 units/mg protein Unit Definition: One unit is defined as the amount of enzyme that will catalyze the formation of 1.0 mol ATP from APS and inorganic pyrophosphate per min at 30°C, pH 8.0.