Evidence for NQO1 and NQO2 catalyzed reduction of ortho- and para-quinone methides.
quinone oxidoreductase (NQO1) and NRH:quinone oxidoreductase 2 (NQO2) catalyze the two-electron reduction of quinones and thereby prevent generation of toxic radicals. Quinone methides (QMs) covalently react with cellular macromolecules to form DNA adducts and/or protein conjugates resulting in toxicity and carcinogenesis. Based on similar structural features of quinones and QMs, it is logical to assume that NQO1 and/or NQO2 could also catalyze the two-electron reduction of QMs. However, hitherto the reduction of QMs, as both endogenous and/or exogenous biological substrates, by either NQO1/NQO2 has never been demonstrated. Here we show for the first time that both NQO1 and NQO2 can catalyze the reduction of electrophilic ortho-/para-QMs. The involvement of the enzyme in the reduction of p-cresol quinone methide (PCQM) and o-cresol quinone methide (OCQM) was demonstrated by reappearance of NQO1/NQO2-FAD peak at 450 nm after addition of the QMs to the assay mixture. Further reduction of methides by NQO1/NQO2 was confirmed by analyzing the assay mixture by tandem mass spectrometry. Preliminary kinetic studies show that NQO2 is faster in reducing QMs than its homolog NQO1, and moreover, ortho-QMs are reduced faster than para-QMs. Enzyme-substrate docking studies showed results consistent with enzyme catalysis. Thus, NQO1/NQO2 can play a significant role in deactivation of QMs.
Department of Nutrition, University of California , Davis, CA , USA.
H R
HR
Kucera
M
M
Livingstone
C G
CG
Moscoso
N W
NW
Gaikwad
D006801:Humans; D045563:Indolequinones / Q000737:chemistry / Q000378:metabolism*; D013058:Mass Spectrometry; D056004:Molecular Dynamics Simulation; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000737:chemistry / Q000378:metabolism*; D011808:Quinone Reductases / Q000737:chemistry / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet
D045563:Indolequinones; D009243:NAD; C068040:quinone methide; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human; C419642:NRH - quinone oxidoreductase2; D011808:Quinone Reductases