MITOCHONDRIAL RESPIRATORY SUPERCOMPLEXES LIMIT REACTIVE OXYGEN SPECIES (ROS) PRODUCTION.

The mitochondrial respiratory chain is organized as supercomplexes (SC) which confer substrate channeling and scaffold for assembly/stability of Complex I (CI). Some studies suggested that SC may also prevent excessive reactive oxygen species (ROS) production from CI and Complex III (CIII) but failed to show if SC dissociation is a cause or a consequence. In the present study we addressed this issue in proteoliposomes containing CI and CIII from bovine heart mitochondria. When proteoliposomes are at low lipid/protein ratio, BN-PAGE shows that CI and CIII are present as SC. Their treatment with dodecyl maltoside disassembles SC into CI and CIII. Alternatively, SC are not formed when proteoliposomes are at high lipid/protein ratio. NADH-cytochrome c reductase activity (CoQ10 channeling) is dramatically decreased when SC are disassembled, while CI is functional active. These results show that CoQ10 channeling shifts to a less efficient pool behavior while reconstituted proteoliposomes at high lipid/protein ratio with 20% cardiolipin restores CoQ10 channeling. Under disruption or prevention of SC assembly we observe a strong increase of ROS production from CI, detected with dichlorofluorescein. This is the first demonstration that dissociation of SC is a cause of oxidative stress from CI that may perpetuate a vicious cycle of ROS generation and bioenergetics failure.