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

The oxidation of linoleic acid by soybean lipoxygenase-1 (LOX-1) was inhibi ted in a time-dependent manner by 4-hydroxy-2 (E)-nonenal (HNE), Kinetic an alysis indicated the effect was due to slow-binding inhibition conforming t o an affinity labeling mechanism-based inhibition. After 25 min of preincub ation of LOX-1 with and without HNE, Lineweaver-Burk reciprocal plots indic ated mixed noncompetitive/competitive inhibition. Low concentrations of HNE influenced the electron paramagnetic resonance (EPR) signal of 13(S)-hydro peroxy-9 (Z),11 (E)-octadecadienoic acid (13-HPODE)-generated Fe3+-LOX-1 sl ightly, but higher concentrations completely eliminated the EPR signal indi cating an active site hindered from access by 13-HPODE. HNE may compete for the active site of LOX-1 because its precursor, 4-hydroperoxy-(2 E)-nonena l, is a product of LOX-1 oxidation of (3Z)-nonenal. Also, it was an attract ive 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 ir on active site of LOX-1.