Flavin-containing quinone reductase that catalyzes two-electron reduction of quinones to hydroquinones using either NADH or NADPH as electron donors. In a ping-pong kinetic mechanism, the electrons are sequentially transferred from NAD(P)H to flavin cofactor and then from reduced flavin to the quinone, bypassing the formation of semiquinone and reactive oxygen species (PubMed:8999809, PubMed:1703398, PubMed:7862630). Regulates cellular redox state primarily through quinone detoxification. Reduces components of plasma membrane redox system such as coenzyme Q and vitamin quinones, producing antioxidant hydroquinone forms. In the process may function as superoxide scavenger to prevent hydroquinone oxidation and facilitate excretion (By similarity). Alternatively, can activate quinones and their derivatives by generating redox reactive hydroquinones with DNA cross-linking antitumor potential (By similarity). Acts as a gatekeeper of the core 20S proteasome known to degrade proteins with unstructured regions. Upon oxidative stress, interacts with tumor suppressors TP53 and TP73 in a NADH-dependent way and inhibits their ubiquitin-independent degradation by the 20S proteasome (By similarity). a quinone + H(+) + NADH = a quinol + NAD(+) a quinone + H(+) + NADPH = a quinol + NADP(+) H(+) + NADH + ubiquinone-10 = NAD(+) + ubiquinol-10 H(+) + menadione + NADH = menadiol + NAD(+) kcat is 0.075 min(-1) NADH with as substrate. kcat is 0.074 min(-1) with NADPH as substrate. Homodimer (PubMed:7568029). Interacts with PDLIM4 isoform 2; this interaction stabilizes PDLIM4 isoform 2 in response to oxidative stress and protects it from ubiquitin-independent degradation by the core 20S proteasome (By similarity). Interacts with TP73 (via SAM domain); this interaction is NADH-dependent, stabilizes TP73 in response to oxidative stress and protects it from ubiquitin-independent degradation by the 20S proteasome (By similarity). Interacts with TP53; this interaction is NADH-dependent, stabilizes TP53 in response to oxidative stress and protects it from ubiquitin-independent degradation by the 20S proteasome (By similarity). By polycyclic hydrocarbons (Governed by the aromatic hydrocarbon-responsive (AH) locus). Quinone reductase accepts electrons from both NADH and NADPH with equal efficiency. This protein is inhibited by dicoumarol. Belongs to the NAD(P)H dehydrogenase (quinone) family. PubMed:2480957 sequence seems incorrectly to be attributed to a mouse sequence while it really seems to correspond to the rat sequence.