Scheme 1.

Aerobic and anaerobic reactions catalyzed by the soybean lipoxygenase (LOX)-1 isoenzyme and involved in 4-nitroso-N,N-dimethylaniline (RNO) bleaching or fluorescein (FL) quenching. The aerobic cycle of LOX-1-catalyzed dioxygenation of linoleic acid (LH, highlighted in teal) to 13-hydroperoxy-linoleate (LOOH, highlighted in orange) is shown (continuous line), as well as the secondary anaerobic cycle (dotted line) involving LOX-1 under limited oxygen conditions and generating some reactive species (highlighted in red). These may induce RNO bleaching or FL quenching. This may be inhibited by antioxidant compounds by different mechanisms (green arrows): scavenging one or more radical species; chelating or reducing iron ion; inhibiting the apoenzyme. L^∙, linoleate alkylic radical; LO^∙, linoleate alkoxyl radical; LOO^∙, linoleate peroxyl radical; ¹O₂, singlet oxygen; ^∙OH, hydroxyl radical. “Fe” indicates the non-heme iron atom playing a key role in LOX-1 catalysis. Adapted from Pastore et al. [25].