title: ATP reversible Pi exchange and membrane phosphorylation in sarcoplasmic reticulum vesicles: activation by silver in the absence of a Ca2+ concentration gradient.
abstract: The activation of ATP reversible Pi exchange, normally associated with a Ca2+ concentration gradient in sarcoplasmic reticulum vesicles, can be obtained in "leaky" vesicles in 4-10 mM CaCl2. In the micromolar range, Ag+ activates the ATP reversible Pi exchange two- to fourfold. Similar concentrations of Ag+ promote a parallel inhibition of Ca2+- activated ATP hydrolysis and Ca2+ uptake in intact vesicles. Maximal inhibition of these activities by Ag+ leaves the Mg2+-dependent ATPase unaffected. No net synthesis of ATP was demonstrated in leaky vesicles. The effects of Ag+ depends on the protein concentration and persist after removal of Ag+ from the medium. Membrane phosphorylation from Pi or from ATP is respectively activated or inhibited by Ag+ in reciprocal fashion.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012834:Silver / Q000494:pharmacology*
chemical_list: D010710:Phosphates; D012834:Silver; D004533:Egtazic Acid; D003300:Copper; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium