title: ATP-dependent phosphate transport in sarcoplasmic reticulum and reconstituted proteoliposomes.
abstract: During uptake of Ca2+ by rabbit sarcoplasmic reticulum, about 1 mumol of 32Pi was taken up per mumol 45Ca2+ transported. The uptake of Pi was dependent on external Ca2+, Mg2+ and ATP. Intravesicular Ca2+ did not substitute for external Ca2+. In contrast to the accumulation of Ca2+ which was abolished by the ionophore A23187, the uptake of Pi continued to take place provided sufficient Ca2+ was present in the medium. Thus, a Ca2+ gradient did not seem to be required. Similar observations were made with proteoliposomes reconstituted with membrane preparations of sarcoplasmic reticulum and soybean phospholipids. However, when purified Ca2+ -ATPase was used for reconstitution, there was ATP-dependent Ca2+ uptake but no ATP-dependent Pi transport was observed. These data show that the mechanism of Pi transport cannot be a passive movement in response to a Ca2+ gradient but appears to be catalyzed by a specific protein, which is inactivated during purification of the Ca2+ -ATPase. A protein that catalyzes Pi transport in reconstituted vesicles has been solubilized by extraction of sarcoplasmic reticulum with sodium cholate.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism*; D010761:Phosphorus Radioisotopes; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D008081:Liposomes; D010710:Phosphates; D010761:Phosphorus Radioisotopes; D000001:Calcimycin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium