MetaCyc

Parent Class:

EC-Numbers → 1 -- Oxidoreductases → 1.6 -- Acting on NADH or NADPH → 1.6.5 -- With a quinone or similar compound as acceptor

Synonyms: NADPH₂:quinone reductase

Systematic Name: NADPH:quinone oxidoreductase

Unification Links: BRENDA:1.6.5.5, ENZYME:1.6.5.5, IUBMB-ExplorEnz:1.6.5.5

Reaction:
NADPH + 2 a quinone + H⁺ → NADP⁺ + 2 a semiquinone

Summary:
A zinc enzyme, specific for NADPH. Catalyses the one-electron reduction of certain quinones, with the orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone being the best substrates [Rao92]. Dicoumarol [cf. EC 1.6.5.2 NAD(P)H dehydrogenase (quinone)] and nitrofurantoin are competitive inhibitors with respect to the quinone substrate. The semiquinone free-radical product may be non-enzymically reduced to the hydroquinone or oxidized back to quinone in the presence of O₂ [Rao92]. In some mammals, the enzyme is abundant in the lens of the eye, where it is identified with the protein ζ-crystallin.

Citations: [Duhaiman96, Bazzi01, Tang01]