Reconstitution of adenosine 3'-phosphate 5'-phosphosulfate transporter from rat brain

Adenosine 3'-phosphate 5'-phosphosulfate (PAPS), the "active" sulfate donor for sulfated macromolecules, is synthesized in the cytosolic fraction of rat brains. This molecule is then translocated into the lumen of the Golgi apparatus so that it is available to the sulfotransferase enzymes. The protein responsible for the PAPS translocating activity has been solubilized from vesicles enriched in enzyme markers for the Golgi apparatus and reconstituted into liposomes. In reconstituted liposomes translocating activity has a pH optimum of 7.0 and activity was increased 3-fold by divalent cations, although EDTA produced no inhibition. The affinity of the reconstituted translocator for PAPS showed a Km of 1.2 mM with a Vmax of 14 pmol of PAPS translocated/min/mg of protein. Specificity of the translocator activity was tested with a number of nucleotide analogues and only 3',5'-adenosine diphosphate was a competitive inhibitor. Inhibitors of the mitochondrial ADP/ATP transporter and the red cell anion channel blocked transport of PAPS only at very high concentrations.