H2O2 disposal in cardiolipin-enriched mitochondria is due to increased cytochrome c peroxidase activity.

The mitochondrial electron transport chain is a source of oxygen superoxide anion (O2 - ) that is dismutated to H2O2. Although low levels of ROS are physiologically synthesized during respiration, their increase contributes to cell injury. Therefore, an efficient machinery for H2O2 disposal is essential in mitochondria. In this study, the ability of brain mitochondria to acquire cardiolipin (CL), phosphatidylglycerol (PG), and phosphatidylserine (PS) in vitro through a fusion process was exploited to investigate lipid effects on ROS. MTT assay, oxygen consumption, and respiratory ratio indicated that the acquired phospholipids did not alter mitochondrial respiration and O2 − production from succinate. However, in CL-enriched mitochondria, H2O2 levels where 27% and 47% of control in the absence and in the presence of antimycin A, respectively, suggesting an increase in H2O2 elimination. Concomitantly, cytochrome c (cyt c) was released outside mitochondria. Since free oxidized cyt c acquired peroxidase activity towards H2O2 upon interaction with CL in vitro, a contribution of cyt c to H2O2 disposal in mitochondria through CL conferred peroxidase activity is plausible. In this model, the accompanying CL peroxidation should weaken cyt c-CL interactions, favouring the detachment and release of the protein. Neither cyt c peroxidase activity was elicited by PS in vitro, nor cyt c release was observed in PS-enriched mitochondria, although H2O2 levels were significantly decreased, suggesting a cyt c-independent role of PS in ROS metabolism in mitochondria.