Mitochondrial respiratory complex I – FMN-associated secondary quinone site (Complex I FMN site)

Mitochondrial respiratory complex I (NADH:ubiquinone oxidoreductase) is the entry point for electrons into the respiratory chain, coupling NADH oxidation to proton translocation. The FMN-associated secondary quinone site, also known as Site IF, is located in the peripheral arm of the complex near the flavin mononucleotide cofactor. While the primary Q-site reduces physiological ubiquinone, the FMN-associated site is capable of reducing artificial quinones and serves as a critical hub for the generation of reactive oxygen species (ROS). This site is the primary target for biguanides like metformin, which inhibit the enzyme's activity to modulate cellular energy metabolism and reduce oxidative stress. Targeting this site is central to the management of type 2 diabetes and is being investigated for its potential to selectively disrupt cancer cell metabolism and protect against neurodegeneration.

Other names

Site IFFMN site of Complex INADH-binding site of Complex II-siteDiaphorase site of Complex IFlavin site of Complex I

Inhibition of NADH oxidation, suppression of mitochondrial ROS production, and indirect activation of AMPK through alteration of the ATP/AMP ratio.