The effects of various antioxidants, nitric oxide (NO)- donor compounds and natural polyamines on the dioxygenation reaction catalyzed by soybean (Glycine max) lipoxygenases will be reviewed. Evidence will be presented that chain-breaking antioxidants ascorbic acid, 6-palmitoylascorbic acid and trolox inhibit soybean lipoxygenase-1 in the micromolar range (Ki 27, 3 and 18 μM respectively), whereas nitric oxide (NO)-releasing agents such as sodium nitroprusside and S-nitroso-N-acetylpenicillamine inhibit soybean lipoxygenase-2 with inhibition constants of 525 and 710 μM, respectively. These values correspond to a Ki of NO for lipoxygenase-2 of approximately 0.4 μM. Natural polyamines are shown to inhibit dioxygenase activity of lipoxygenase-1, whereas they are ineffective toward the lipoxygenase-2. The inhibitory power followed the order spermine > spermidine > cadaverine ≥ putrescine. The Ki values of spermine and spermidine for lipoxygenase-1 were 800 and 2700 μM, respectively. The possible physiological significance of these findings will be discussed, in the light of the involvement of the lipoxygenase pathway in biomembrane remodelling and biosynthesis of active biomolecules, such as jasmonic acid and traumatin.
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