The inhibition of the mitochondrial F1FO-ATPase activity when activated by Ca2+opens new regulatory roles for NAD+

The mitochondrial F1FO-ATPase is uncompetitively inhibited by NAD+only when the natural cofactor Mg2+is replaced by Ca2+, a mode putatively involved in cell death. The Ca2+-dependent F1FO-ATPase is also inhibited when NAD+concentration in mitochondria is raised by acetoacetate. The enzyme inhibition by NAD+cannot be ascribed to any de-ac(et)ylation or ADP-ribosylation by sirtuines, as it is not reversed by nicotinamide. Moreover, the addition of acetyl-CoA or palmitate, which would favor the enzyme ac(et)ylation, does not affect the F1FO-ATPase activity. Consistently, NAD+may play a new role, not associated with redox and non-redox enzymatic reactions, in the Ca2+-dependent regulation of the F1FO-ATPase activity.