Mitochondrial Ca -activated F F -ATPase hydrolyzes ATP and promotes the permeability transition pore.

The properties of the mitochondrial F F -ATPase catalytic site, which can bind Mg , Mn , or Ca and hydrolyze ATP, were explored by inhibition kinetic analyses to cast light on the Ca -activated F F -ATPase connection with the permeability transition pore (PTP) that initiates cascade events leading to cell death. While the natural cofactor Mg activates the F F -ATPase in competition with Mn , Ca is a noncompetitive inhibitor in the presence of Mg . Selective F inhibitors (Is-F ), namely NBD-Cl, piceatannol, resveratrol, and quercetin, exerted different mechanisms (mixed and uncompetitive inhibition) on either Ca - or Mg -activated F F -ATPase, consistent with the conclusion that the catalytic mechanism changes when Mg is replaced by Ca . In a partially purified F domain preparation, Ca -activated F -ATPase maintained Is-F 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 Ca -activated F F -ATPase and the PTP, and, in turn, on consequences, such as physiopathological cellular changes.