| Abstract: | The translocation of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) across rat liver Golgi-derived vesicles has been studied. Vesicles of the same topographical orientation as in vivo were incubated with a mixture of adenine-8-3H]PAPS and 35S]PAPS. The tritium to radiolabeled sulfur ratio of the incubation medium was 1.73 +/- 0.03 while that in the vesicles was 1.82 +/- 0.13. This strongly suggests that the entire PAPS molecule was being translocated across the Golgi vesicle membrane even though intact PAPS could not be detected within the vesicles. Translocation of PAPS resulted in accumulation of solutes within vesicles. This accumulation was temperature dependent, saturable (apparent Km = 0.7 microM; Vmax = 25 pmol/mg of protein/10 min), and inhibited by the substrate analogue 3',5'-ADP but not by 2',5'-ADP. Translocation of PAPS was inhibited following treatment of Golgi vesicles with Pronase under conditions in which the activity of a lumenal Golgi membrane marker such as sialyltransferase was not. This result is consistent with the existence of a PAPS carrier protein, portions of which face the cytoplasmic side of the Golgi membrane. |
