Quinol-fumarate reductase (QFR)

Quinol-fumarate reductase (QFR) in Escherichia coli is a four-subunit integral membrane enzyme complex responsible for catalyzing the final step of anaerobic respiration by reducing fumarate to succinate, using reduced quinones (primarily menaquinol) as electron donors. It is functionally distinct from the homologous succinate dehydrogenase (aerobic, Complex II), with QFR preferentially operating under anaerobic conditions to enable E. coli growth when fumarate is the terminal electron acceptor. QFR's structure includes flavoprotein, iron-sulfur protein, and membrane-spanning subunits with multiple redox-active cofactors, facilitating electron transfer from the membrane-bound quinol through iron-sulfur clusters to FAD, and finally to fumarate. Inhibitors that block the quinol-binding site (e.g., HQNO) have been structurally characterized, demonstrating druggability of this bacterial respiratory target. QFR is essential for E. coli's energy metabolism in low-oxygen environments and provides a model for respiratory adaptation in anaerobes.

Other names

Fumarate reductase (quinol)Menaquinol:fumarate oxidoreductaseFrdABCD (gene complex)

Competitive inhibition of quinol binding site, blocking electron transfer and fumarate reduction