Novel difference in IF1 reactivity to Zn2+ in rabbit versus rat cardiomyocytes, mitochondria, and submitochondrial particles.

Zn2+ has a paradoxical effect on IF1-ATPase interaction in cardiac muscle mitochondria in so-called slow heart-rate mammalian species like rabbit. In such slow heart-rate mammalian species, it completely prevents IF1-mediated ATPase inhibition regardless of pH while concomitantly causing full IF1 binding to the ATPase, again, regardless of pH (Rouslin et al. (1993) J. Bioenerget. Biomembr. 25, 297-306). While our earlier study suggested that there are two kinds of IF1-ATPase interaction, a docking interaction and an ATPase inhibitory interaction with Zn2+ promoting docking and interfering with inhibition, it did not yield information on whether Zn2+ interacted primarily with IF1, with the ATPase, or with both. In the present study we show that, in contrast to its effects in rabbit cardiomyocytes, mitochondria, and SMP in which Zn2+ fully blocked IF1-mediated ATPase inhibition, Zn2+ actually enhanced ATPase inhibition in rat cardiomyocytes, although the extent of this effect was limited by the low level of IF1 in rat cardiomyocytes. Moreover, Zn2+ had no effect on IF1-mediated ATPase inhibition in rat heart mitochondria and, as suggested by inter and intra-species IF1 binding to SMP, the different effects of Zn2+ in rabbit versus those in rat appear to be mediated primarily through the different reactivities of rabbit and rat IF1 to Zn2+.