Ubiquinol-cytochrome c reductase cytochrome b subunit (CYTB)

The Ubiquinol-cytochrome c reductase cytochrome b subunit, commonly known as Cytochrome b, is the only subunit of the mitochondrial respiratory chain complex III (bc1 complex) encoded by the mitochondrial genome (UniProtKB - P00156). It serves as the central catalytic core of the complex, facilitating the transfer of electrons from ubiquinol to cytochrome c via the Q-cycle mechanism, which is coupled to proton translocation across the inner mitochondrial membrane (Meunier et al., 2004). This process is vital for maintaining the electrochemical gradient required for ATP synthesis. In humans, mutations in the MT-CYB gene are linked to various mitochondrial pathologies, including exercise intolerance and Leber hereditary optic neuropathy (StatPearls, 2023). Cytochrome b is a highly validated therapeutic target, particularly in the treatment of parasitic infections like malaria. The drug atovaquone acts as a potent and selective inhibitor of the parasite's Cytochrome b at the Qo site, effectively disrupting the respiratory chain and pyrimidine biosynthesis (Srivastava et al., 1999). However, the clinical utility of such drugs is often challenged by the rapid emergence of point mutations in the cytochrome b gene that confer high-level resistance. Beyond human medicine, this subunit is a primary target for several classes of agricultural fungicides, such as strobilurins, highlighting its universal importance in aerobic energy metabolism (Fisher et al., 2020).

Other names

Cytochrome bMT-CYBComplex III subunit 3Ubiquinol-cytochrome c oxidoreductase cytochrome b subunitMitochondrially encoded cytochrome b

Inhibition of the ubiquinol oxidation (Qo) or ubiquinone reduction (Qi) sites within the cytochrome bc1 complex, leading to the collapse of the mitochondrial membrane potential and cessation of ATP production.