Preferential nitrite inhibition of the mitochondrial F1FO-ATPase activities when activated by Ca2 + in replacement of the natural cofactor Mg2 +

BackgroundThe mitochondrial F₁F_O-ATP synthase has not only the known life function in building most cellular ATP, but also, as recently hinted, an amazing involvement in cell death. Accordingly, the two-faced enzyme complex, which catalyzes both ATP synthesis and ATP hydrolysis, has been involved in the mitochondrial permeability transition, the master player in apoptosis and necrosis. Nitrite, a cellular nitric oxide reservoir, has a recognized role in cardiovascular protection, through still unclear mechanisms.MethodsIn swine heart mitochondria the effect of nitrite on the F₁F_O-ATPase activity activated by Ca^2 +, henceforth defined as Ca-ATPase(s), or by the natural cofactor Mg^2 +, was investigated by evaluating ATP hydrolysis under different assay conditions.ResultsCa^2 + is far less efficient than the natural cofactor Mg²⁺ in the ATPase activation. However, when activated by Ca²⁺ the ATPase activity is especially responsive to nitrite, which acts as uncompetitive inhibitor and up to 2 mM inhibits the Ca²⁺-activated-ATPase(s), probably by promoting dytirosine formation on the enzyme proteins, leaving the Mg-ATPase(s) unaffected. Most likely these ATPases refer to the same F₁F_O complex, even if coexistent ATPases may overlap.ConclusionsThe preferential inhibition by nitrite of the Ca-ATPase(s), due to post-translational tyrosine modifications, may prevent the calcium-dependent functionality of the mitochondrial F₁F_O complex and related events.General significanceIn mitochondria the preferential inhibition of the Ca-ATPase activity/ies by nitrite concentrations which do not affect the coexistent Mg-ATPase(s) may quench the negative events linked to the calcium-dependent functioning mode of the F₁F_O complex under pathological conditions.