Oxygenation of (3Z)-alkenal to (2E)-4-hydroxy-2-alkenal in soybean seed (Glycine max L.).
(3Z)-Alkenals, such as (3Z)-hexenal and (3Z)-nonenal, are produced from polyunsaturated fatty acids via lipoxygenase and hydroperoxide lyase catalysis, but in soybeans (Glycine max L.) (3Z)-alkenals have a fleeting existence. In this study it was shown that soybean seeds possess two pathways that metabolize (3Z)-alkenals. One is a soluble (3Z):(2E)-enal isomerase that transformed (3Z)-hexenal and (3Z)-nonenal into the corresponding (2E)-alkenals. The other was a membrane-bound system that converted (3Z)-hexenal and (3Z)-nonenal into (2E)-4-hydroxy-2-hexenal and (2E)-4-hydroxy-2-nonenal, respectively. The latter conversion was shown to absorb O2 with a pH optimum of 9.5. Little effect observed with lipoxygenase inhibitors suggested that oxidation was not catalyzed by lipoxygenase. Instead, a specific (3Z)-alkenal oxygenase was implicated in forming intermediate alkenal hydroperoxides. Hydroperoxide-dependent peroxygenase (epoxygenase) is known to reduce hydroperoxides to their corresponding hydroxides and is also known to be inhibited by hydrogen peroxide preincubation. Consequently, intermediate 4-hydroperoxy-2-alkenals could be observed after inhibiting hydroperoxide-dependent peroxygenase by preincubation with hydrogen peroxide. Because 4-hydroxy-2-alkenals are potent toxins, these compounds may be produced as nonvolatile plant defensive substances.
Takamura
H
H
Department of Food Science and Nutrition, Nara Women's University, Japan.
Gardner
H W
HW
D000447:Aldehydes / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007535:Isomerases / Q000378:metabolism*; D008084:Lipoxygenase / Q000378:metabolism; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D010940:Plant Proteins / Q000378:metabolism*; D013025:Glycine max / Q000378:metabolism*; D019745:cis-trans-Isomerases
D000447:Aldehydes; D004791:Enzyme Inhibitors; D016859:Lipoxygenase Inhibitors; D008565:Membrane Proteins; D010940:Plant Proteins; C080589:3-nonenal; D006861:Hydrogen Peroxide; D006899:Mixed Function Oxygenases; D008084:Lipoxygenase; C022333:peroxygenase; D007535:Isomerases; C101856:(3Z)-(2E) enal isomerase; D019745:cis-trans-Isomerases; C027576:4-hydroxy-2-nonenal; D010100:Oxygen