Mitochondrial respiratory chain complexes I, II, and III (MRC Complexes I-III)

The mitochondrial respiratory chain complexes I, II, and III are essential multi-subunit enzyme assemblies located within the inner mitochondrial membrane that facilitate the electron transport chain (ETC) (UniProt: P03886, NCBI: 6389, PubMed: 10654911). Complex I (NADH:ubiquinone oxidoreductase) initiates the process by oxidizing NADH and pumping protons across the membrane, while Complex II (Succinate dehydrogenase) serves as a secondary entry point for electrons from the citric acid cycle. Complex III (Cytochrome bc1 complex) continues the relay by transferring electrons from ubiquinol to cytochrome c, further contributing to the proton gradient. This electrochemical gradient is ultimately harnessed by ATP synthase to produce the majority of cellular ATP through oxidative phosphorylation. Dysfunction in these complexes is a hallmark of many mitochondrial and neurodegenerative diseases, such as Parkinson's and Leigh syndrome, due to impaired energy production and increased oxidative stress (StatPearls: 2023). Pharmacologically, these complexes are targeted by drugs like metformin for metabolic control or novel inhibitors like IACS-010759 for cancer therapy, though such interventions carry risks of systemic toxicity and lactic acidosis (PubMed: 11069076, Nature Medicine: 2018).

Other names

Electron transport chain complexes I, II, and IIINADH:ubiquinone oxidoreductase (Complex I)Succinate dehydrogenase (Complex II)Cytochrome bc1 complex (Complex III)Ubiquinol-cytochrome c reductase (Complex III)

Inhibition of electron transfer within the respiratory chain, leading to the disruption of the proton motive force, reduction in ATP production, and modulation of cellular redox states or induction of apoptosis (PubMed: 11069076, Nature Medicine: 2018).