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

The properties of the mitochondrial F1FO-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 F1FO-ATPase connection with the permeability transition pore (PTP) that initiates cascade events leading to cell death. While the natural cofactor Mg2+ activates the F1FO-ATPase in competition with Mn2+, Ca2+ is a noncompetitive inhibitor in the presence of Mg2+. Selective F-1 inhibitors (Is-F-1), namely NBD-Cl, piceatannol, resveratrol, and quercetin, exerted different mechanisms (mixed and uncompetitive inhibition) on either Ca2+- or Mg2+-activated F1FO-ATPase, consistent with the conclusion that the catalytic mechanism changes when Mg2+ is replaced by Ca2+. In a partially purified F-1 domain preparation, Ca2+-activated F-1-ATPase maintained Is-F-1 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 F1FO-ATPase and the PTP, and, in turn, on consequences, such as physiopathological cellular changes.