Mitochondrial electron transport chain complexes I-IV and inner mitochondrial membrane (ETC)

The mitochondrial electron transport chain (ETC) consists of four multi-subunit enzyme complexes (Complex I, II, III, and IV) embedded within the inner mitochondrial membrane (IMM) [StatPearls, 2023]. Its primary biological function is to facilitate oxidative phosphorylation, where electrons from NADH and FADH2 are transferred through the complexes to molecular oxygen, creating a proton gradient that drives ATP production [Molecular Biology of the Cell, 2002]. This system is also a major source of reactive oxygen species (ROS) and plays a critical role in regulating apoptosis and cellular metabolism [PubMed, 2017]. Mutations or dysfunction in ETC components are central to primary mitochondrial diseases, such as Leigh syndrome and Leber hereditary optic neuropathy, and contribute to the pathogenesis of neurodegenerative disorders like Parkinson's disease [NIH, 2024]. Pharmacologically, the ETC is targeted by drugs like metformin, which inhibits Complex I to improve insulin sensitivity, and is the site of action for various toxins like cyanide and carbon monoxide that inhibit Complex IV [Bridges et al., 2014]. Therapeutic interventions often aim to either modulate metabolic flux or protect against oxidative damage resulting from ETC inefficiency [Journal of Clinical Investigation, 2013].

Other names

Respiratory chainOXPHOS systemMitochondrial respiratory chainElectron transport chainInner mitochondrial membrane

Drugs targeting this system primarily act through the inhibition of specific complexes (e.g., Metformin inhibiting Complex I) to alter the AMP/ATP ratio and activate downstream signaling like AMPK [Bridges et al., 2014]. Other agents, such as Idebenone, act as electron carriers to bypass defective complexes and restore electron flow to Complex III [NCBI, 2021]. Toxicants like cyanide and carbon monoxide bind to the heme center of Cytochrome c oxidase (Complex IV), halting the respiratory chain and causing cellular hypoxia [StatPearls, 2023].