The NADPH:Quinone Oxidoreductase P1-ζ-crystallin in Arabidopsis Catalyzes the α,β-Hydrogenation of 2-Alkenals: Detoxication of the Lipid Peroxide-Derived Reactive Aldehydes

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Abstract
P1-ζ-crystallin (P1-ZCr) is an oxidative stress-induced NADPH:quinone oxidoreductase in Arabidopsis thaliana, but its physiological electron acceptors have not been identified. We found that recombinant P1-ZCr catalyzed the reduction of 2-alkenals of carbon chain C3-C9 with NADPH. Among these 2-alkenals, the highest specificity was observed for 4-hydroxy-(2E)-nonenal (HNE), one of the major toxic products generated from lipid peroxides. (3Z)-Hexenal and aldehydes without α,β-unsaturated bonds did not serve as electron acceptors. In the 2-alkenal molecules, P1-ZCr catalyzed the hydrogenation of α,β-unsaturated bonds, but not the reduction of the aldehyde moiety, to produce saturated aldehydes, as determined by gas chromatography/mass spectrometry. We propose the enzyme name NADPH:2-alkenal α,β-hydrogenase (ALH). A major portion of the NADPH-dependent HNE-reducing activity in A. thaliana leaves was inhibited by the specific antiserum against P1-ZCr, indicating that the endogenous P1-ZCr protein has ALH activity. Because expression of the P1-ZCr gene in A. thaliana is induced by oxidative stress treatments, we conclude that P1-ZCr functions as a defense against oxidative stress by scavenging the highly toxic, lipid peroxide-derived α,β-unsaturated aldehydes.