Effect of 4‐hydroxy‐2(E)‐nonenal on soybean lipoxygenase‐1

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Abstract
The oxidation of linoleic acid by soybean lipoxygenase‐1 (LOX‐1) was inhibited in a time‐dependent manner by 4‐hydroxy‐2‐(E)‐nonenal (HNE). Kinetic analysis indicated the effect was due to slow‐binding inhibition conforming to an affinity labeling mechanism‐based inhibition. After 25 min of preincubation of LOX‐1 with and without HNE, Lineweaver‐Burk reciprocal plots indicated mixed noncompetitive/competitive inhibition. Low concentrations of HNE influenced the electron paramagnetic resonance (EPR) signal of 13(S)‐hydroperoxy‐9(Z), 11(E)‐octadecadienoic acid (13‐HPODE)‐generated Fe3+‐LOX‐1 slightly, but higher concentrations completely eliminated the EPR signal indicating an active site hindered from access by 13‐HPODE. HNE may compete for the active site of LOX‐1 because its precursor, 4‐hydroperoxy‐(2E)‐nonenal, is a product of LOX‐1 oxidation of (3Z)‐nonenal. Also, it was an attractive hypothesis to suggest that HNE may disrupt the active site by forming a Michael adduct with one or more of the three histidines that ligate the iron active site of LOX‐1.