Mitochondrial Ca2+ -activated F1 FO -ATPase hydrolyzes ATP and promotes the permeability transition pore

The properties of the mitochondrial F₁ F_O -ATPase catalytic site, which can bind Mg²⁺ , Mn²⁺ , or Ca²⁺ and hydrolyze ATP, were explored by inhibition kinetic analyses to cast light on the Ca²⁺ -activated F₁ F_O -ATPase connection with the permeability transition pore (PTP) that initiates cascade events leading to cell death. While the natural cofactor Mg²⁺ activates the F₁ F_O -ATPase in competition with Mn²⁺ , Ca²⁺ is a noncompetitive inhibitor in the presence of Mg²⁺ . Selective F₁ inhibitors (Is-F₁ ), namely NBD-Cl, piceatannol, resveratrol, and quercetin, exerted different mechanisms (mixed and uncompetitive inhibition) on either Ca²⁺ - or Mg²⁺ -activated F₁ F_O -ATPase, consistent with the conclusion that the catalytic mechanism changes when Mg²⁺ is replaced by Ca²⁺ . In a partially purified F₁ domain preparation, Ca²⁺ -activated F₁ -ATPase maintained Is-F₁ sensitivity, and enzyme inhibition was accompanied by the maintenance of the mitochondrial calcium retention capacity and membrane potential. The data strengthen the structural relationship between Ca²⁺ -activated F₁ F_O -ATPase and the PTP, and, in turn, on consequences, such as physiopathological cellular changes.