Kinetic properties of the mitochondrial FF-ATPase activity elicited by Ca in replacement of Mg.

The mitochondrial F-ATPase can be activated either by the classical cofactor Mg or, with lower efficiency, by Ca. The latter may play a role when calcium concentration rises in mitochondria, a condition associated with cascade events leading to cell death. Common and distinctive features of these differently activated mitochondrial ATPases were pointed out in swine heart mitochondria. When Ca replaces the natural cofactor Mg, the enzyme responsiveness to the transmembrane electrochemical gradient and to the classical F-ATPase inhibitors DCCD and oligomycin as well as the oligomycin sensitivity loss by thiol oxidation, are maintained. Consistently, the two mitochondrial ATPases apparently share the FF complex basic structure and mechanism. Peculiar cation-dependent properties, which may affect the F catalytic mechanism and/or the F proton binding site features, may be linked to a different physiological role of the mitochondrial Ca-activated F-ATPase with respect to the Mg-activated F-ATPase.