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EC 1.6.5.5 Details

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EC number

1.6.5.5

Accepted name

NADPH:quinone reductase

Reaction

NADPH + H⁺ + 2 quinone = NADP⁺ + 2 semiquinone

Other name(s)

NADPH₂:quinone reductase

Systematic name

NADPH:quinone oxidoreductase

CAS registry number

9032-20-6

Comment

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 [1]. 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 [1]. In some mammals, the enzyme is abundant in the lens of the eye, where it is identified with the protein ζ-crystallin.

History

created 1999

EC Tree

1 Oxidoreductases

1.1 Acting on the CH-OH group of donors

1.1.1 With NAD⁺ or NADP⁺ as acceptor

1.1.2 With a cytochrome as acceptor

1.1.3 With oxygen as acceptor

1.1.4 With a disulfide as acceptor

1.1.5 With a quinone or similar compound as acceptor

1.1.7 With an iron-sulfur protein as acceptor

1.1.9 With a copper protein as acceptor

1.1.98 With other, known, physiological acceptors

1.1.99 With unknown physiological acceptors

1.2 Acting on the aldehyde or oxo group of donors

1.3 Acting on the CH-CH group of donors

1.4 Acting on the CH-NH₂ group of donors

1.5 Acting on the CH-NH group of donors

1.6 Acting on NADH or NADPH

1.6.1 With NAD⁺ or NADP⁺ as acceptor

1.6.2 With a heme protein as acceptor

1.6.3 With oxygen as acceptor

1.6.4 With a disulfide as acceptor (deleted sub-subclass)

1.6.5 With a quinone or similar compound as acceptor

1.6.5.1 created 1961, deleted 1965

1.6.5.2 NAD(P)H dehydrogenase (quinone)

1.6.5.3 NADH:ubiquinone reductase (H⁺-translocating)

1.6.5.4 monodehydroascorbate reductase (NADH)

1.6.5.5 NADPH:quinone reductase

1.6.5.6 p-benzoquinone reductase (NADPH)

1.6.5.7 2-hydroxy-1,4-benzoquinone reductase

1.6.5.8 NADH:ubiquinone reductase (Na⁺-transporting)

1.6.5.9 NADH:quinone reductase (non-electrogenic)

1.6.5.10 NADPH dehydrogenase (quinone)

1.6.5.11 NADH dehydrogenase (quinone)

1.6.5.12 demethylphylloquinone reductase

1.6.6 With a nitrogenous group as acceptor

1.6.7 With an iron-sulfur protein as acceptor (deleted sub-subclass)

1.6.8 With a flavin as acceptor (deleted sub-subclass)

1.6.99 With unknown physiological acceptors

1.6.99.1 NADPH dehydrogenase

1.6.99.2 created 1961 as EC 1.6.5.2, transferred 1965 to EC 1.6.99.2, deleted 2005

1.6.99.3 NADH dehydrogenase

1.6.99.4 created 1965, deleted 1972

1.6.99.5 NADH dehydrogenase (quinone)

1.6.99.6 NADPH dehydrogenase (quinone)

1.6.99.7 created 1972, modified 1981 (EC 1.6.99.10 created 1978, incorporated 1981), deleted 2003

1.6.99.8 created 1972, deleted 2002

1.6.99.9 created 1972, deleted 2002

1.6.99.10 created 1978, deleted 1981

1.6.99.11 created 1989, deleted 2002

1.6.99.12 created 1989, deleted 2002

1.6.99.13 created 1992, deleted 2002

1.7 Acting on other nitrogenous compounds as donors

1.8 Acting on a sulfur group of donors

1.9 Acting on a heme group of donors

1.10 Acting on diphenols and related substances as donors

1.11 Acting on a peroxide as acceptor

1.11.1 Peroxidases

1.11.2 Peroxygenases

1.12 Acting on hydrogen as donor

1.13 Acting on single donors with incorporation of molecular oxygen (oxygenases)

1.14 Acting on paired donors, with incorporation or reduction of molecular oxygen

1.15 Acting on superoxide as acceptor

1.16 Oxidizing metal ions

1.17 Acting on CH or CH₂ groups

1.18 Acting on iron-sulfur proteins as donors

1.19 Acting on reduced flavodoxin as donor

1.20 Acting on phosphorus or arsenic in donors

1.21 Catalysing the reaction X-H + Y-H = X-Y

1.21.1 With NAD⁺ or NADP⁺ as acceptor

1.21.3 With oxygen as acceptor

1.21.4 With a disulfide as acceptor

1.21.98 With other, known, physiological acceptors

1.21.99 With unknown physiological acceptors

1.22 Acting on halogen in donors

1.23 Reducing C-O-C group as acceptor

1.97 Other oxidoreductases

1.98 Enzymes using H₂ as reductant (deleted subclass)

1.99 Other enzymes using O₂ as oxidant (deleted subclass)

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Release 2023.1 (January 2023)