Quinone Reductase NQO

These enzymes eatalyze the reduction of quinones to hydroquinones (both para and ortho) 

Similarly, iminoquinones can be reduced, and the enzymes can also reduce nitro compounds and azo dyes (Ross, 1997). 

NQOl was first characterized as DT diaphorase, with diaphorase being an older term for an enzyme that catalyzes electron transfer from pyridine nucleotides. DT indicated that this enzyme could accept electrons from NADH (formerly termed DPNH) or NADPH (formerly TPNH). Some of the other early work was unclear but the location of the enzyme is cytosolic (Huang et al., 1979). This is a flavoprotein that reduces substrates. In contrast to NADPH-P450 reductase, most NQO reactions are 2-electron reductions, avoiding the generation of radicals. However, the product hydroquinones may react with O2 to generate 2 .  

NQOl is inducible via both the Ah receptor and the ARE pathways (Ross, 1997). Dicoumarol is a long-established potent inhibitor of NQO. A second gene, NQ02 is found in humans (Jaiswal, 1994). A related p53-regulated gene with considerable sequence identity has been discovered (PIG3) (Nicholls et al., 2004) but no redox function has yet been identified. 

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