Quinone reductase acts as a redox switch of the 20S yeast proteasome.

The proteasome has an essential function in the intracellular degradation of protein in eukaryotic cells. We found that the dimeric quinone reductase Lot6 uses the flavin mononucleotide (FMN)-binding site to bind to the 20S proteasome with a 1:2 stoichiometry-that is, one 20S proteasome molecule can associate with two quinone reductases. Furthermore, reduction of the FMN cofactor by either NADH or light irradiation results in the binding of the b-Zip transcription factor Yap4 to the Lot6-proteasome complex, indicating that recruitment of the transcription factor depends on the redox state of the quinone reductase.

Conservation of NADPH utilization by chorismate synthase and its implications for the evolution of the shikimate pathway.

The shikimate pathway is essential for the biosynthesis of aromatic compounds. The seventh and last step is catalysed by chorismate synthase, which has an absolute requirement for reduced FMN in its active site. There are two classes of this enzyme, which are distinguished according to the origin of the reduced cofactor.

Lot6p from Saccharomyces cerevisiae is a FMN-dependent reductase with a potential role in quinone detoxification.

NAD(P)H:quinone acceptor oxidoreductases are flavoenzymes expressed in the cytoplasm of many tissues and afford protection against the cytotoxic effects of electrophilic quinones by catalyzing a strict two-electron reduction. Such enzymes have been reported from several mammalian sources, e.g.