Flavocytochrome b2 (FCB2) FMN-binding domain. FCB2 (AKA L-lactate:cytochrome c oxidoreductase) is a respiratory enzyme located in the intermembrane space of fungal mitochondria which catalyzes the oxidation of L-lactate to pyruvate. FCB2 also participates in a short electron-transport chain involving cytochrome c and cytochrome oxidase which ultimately directs the reducing equivalents gained from L-lactate oxidation to oxygen, yielding one molecule of ATP for every L-lactate molecule consumed. FCB2 is composed of 2 domains: a C-terminal flavin-binding domain, which includes the active site for lacate oxidation, and an N-terminal b2-cytochrome domain, required for efficient cytochrome c reduction. FCB2 is a homotetramer and contains two noncovalently bound cofactors, FMN and heme per subunit.
Jiyao W et al.(2023). "The conserved domain database in 2023.",