NQO1 (NAD(P)H dehydrogenase, quinone 1)

NQO1 catalyzes obligate two electron reduction of a wide variety of substrates. The most efficient substrates are quinones but the enzyme will also reduce quinoneimines, nitro and azo compounds. The enzyme functions via a hydride transfer mechanism and requires a pyridine nucleotide cofactor. Reduction proceeds with equal facility with both NADH and NADPH. NQO1 can generate antioxidant forms of both vitamin E and ubiquinone after free radical attack. The capability to protect cells from oxidative challenge and the ability to reduce quinones via an obligate two electron mechanism, which precludes generation of reactive oxygen radicals, demonstrates that NQO1 is a chemoprotective enzyme. Certain compounds such as antitumor quinones, however, can be bioactivated by two electron reduction and in these cases NQO1 serves as an activating enzyme. Because of the high levels of NQO1 in certain tumors, this has led to an interest in designing compounds which can be efficiently bioactivated by NQO1 as antitumor agents.