title: Vanadate inhibition of ATP-dependent H+ transport in membrane vesicles from turtle bladder epithelial cells.
abstract: The ATP-dependent proton transport into vesicles of a mixed membrane fraction obtained from turtle bladder epithelial cells consists of at least two kinetically defined moieties: one, which is maximally inhibited by 25% with nanomolar levels of vanadate, but not inhibited at all with equimolar levels of N-ethylmaleimide, and another, which is maximally inhibited by 70% with micromolar levels of N-ethylmaleimide and by 25% with equimolar levels of vanadate. In contrast to the transport function, the associated enzymatic function (the ouabain-resistant ATPase activity) in these membranes, not inhibited by nanomolar levels of vanadate or N-ethylmaleimide, is maximally inhibited by 40% with micromolar levels of vanadate and by 13% with equimolar levels of N-ethylmaleimide. Independent of these kinetic differences between the enzyme and the transport functions, membranes containing the N-ethylmaleimide-sensitive proton transport function are electrophoretically separable from those containing the vanadate-sensitive transport function. For example, the kinetically defined, vanadate-sensitive proton transport function is recovered exclusively and kinetically identified in one of four electrophoretic membrane fractions, EF-II; while the N-ethylmaleimide-sensitive function is recovered in EF-III as well as in EF-II. Membranes of EF-IV, maximally enriched in ouabain-resistant ATPase activity, possess no proton transport function at all, even in the absence of N-ethylmaleimide or vanadate. Additional data under in vivo as well as under in vitro conditions are required to prove that the vanadate-sensitive proton transport in these vesicles is an in vitro manifestation of the mechanism responsible for generating the vanadate-sensitive luminal acidification process under in vivo conditions in the intact turtle bladder.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004848:Epithelium / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011522:Protons; D001743:Urinary Bladder / Q000378:metabolism*; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology*
chemical_list: D008081:Liposomes; D011522:Protons; D014639:Vanadium; D014638:Vanadates; D010042:Ouabain; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D005033:Ethylmaleimide