Hydroperoxyoctadecadienoic acid

Galliard and Phillips 144) have found that homogenates of potato tubers contain an enzyme which converts the primary lipoxygenase product of linoleic acid, the 9-D-hydroperoxyoctadecadienoic acid, into an 18-carbon ether (Figure 3). Here too, cleavage of the Gig chain must occur. The formation and role of possible cleavage products from linoleic and linolenic acids in aroma and physiology of plant tissues have already been mentioned. 

The oxidation of AA at C-15 is catalyzed by 15-LOXl, a soluble 661 amino acid-containing protein with a molecular weight of 74,673. Many cells express this enzyme that also efficiently oxidizes linoleic acid to 13-hydroperoxyoctadecadienoic acid and, to a lesser extent, 9-hydroperoxyoctadecadienoic acid because of broad substrate specificity to both 12-HpETE and 15-HpETE [31]. One distinguishing feature of 15-LOXl is that it can oxidize A A esterified to membrane phospholipids, thus forming esterified 15-HpETE. Expression of 15-LOXl is enhanced by several interleukins, suggesting a role of this enzyme in events such as atherosclerosis. 

HETE. The 15-lipoxygenase (15-LOX) has been the most extensively characterized pathway in the reticulocytes, leukocytes, and airway epidermal cells (24-27). An outline in Figure 5 shows that 15-LOX can, on the one hand, catalyze the abstraction of a proton from C-13 of 20-carbon AA to produce 155-hydroperoxyeicosatetraenoic acid (155-HPETE), whereas on the other hand, the 18-carbon linoleic acid is converted mainly to 13-hydroperoxyoctadecadienoic acid (13-HPODE) and 9-hydroperoxy-10,12- , Z-octadecadienoic acid (9-HPODE) in the ratio of 10 1 (28). Both the 155-HPETE (intermediate) from AA and 13-HPODE (intermediate) from linoleic acid can be further metabolized by glutathione peroxidase to mainly monohydroxylated 15S-HETE and 13-hydroxy-octadecadienoic acid (HODE), respectively. 

Fig. 5. Generation of 155-hydroxyeicosatetraenoic acid (HETE) and 13-hydroxyoctadecadienoic acid (HODE) by 15-lipoxyge-nase (LOX)-1 and -2. HPETE, hydroperoxyeicosatetraenoic acid HPODE, hydroperoxyoctadecadienoic acid.

The formation of the product of the linoleic acid oxidation, 13-hydroperoxyoctadecadienoic acid (HPOD), was maximal at pH 9.0. The enzymatic activity of immobilized LOX in... 

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