Human reticulocyte 15-lipoxygenase

Figure 6. Stimulation by human LDL of the arachidonic acid oxidation catalyzed by C-15 animal lipoxygenase (reticulocyte lipoxygenase) (1), in the absence of LDL (2), in the presence of LDL.

Wecksler, A. T., V. Kenyon et al. 2008. Substrate specificity changes for human reticulocyte and epithelial 15-lipoxygenases reveal allosteric product regulation. 

It has been reported that a single methionine residue of rabbit reticulocyte 15-lipoxygenase can be oxidized to its sulphoxide by treatment of the enzyme with 13-hydroperoxy-octadecadienoic acid (a 15-lipoxygenase product from linoleic acid) under anaerobic conditions [59]. Since under this condition the enzyme functioned as lipohydroperoxidase , splitting the hydroperoxide, and resulted in self-inactivation , a central role of the methionine residue was presumed for the catalysis of the enzyme. Recently, this particular methionine has been identified as Met-590 in human 15-lipoxygenase and as Met-591 in rabbit 15-lipoxygenase. When Met-590 in the human enzyme is replaced by leucine by the site-directed mutagenesis, the mutant enzyme is still inactivated by 13-hydroperoxyoctadeca-dienoic acid, 15-HpETE or AA. The result shows that the enzyme inactivation is not attributable to methionine oxidation [60]. 

Soybean lipoxygenase-1 also acts as a 15-lipoxygenase for AA, but the amino acid identity between human 15-lipoxygenase and the soybean enzyme is only 22% [77]. cDNA encoding 15-lipoxygenase cloned from human bronchus cDNA library [78] is identical with that from human reticulocyte cDNA library [77]. Thus the presence of two forms of 15-lipoxygenase in a human leucocyte preparation [82] awaits further investigation. 

Different isoforms of 15-lipoxygenase have been purified to homogeneity from mammalian sources, including reticulocytes and leukocytes, and complementary DNAs encoding them have been cloned. The reticulocyte 15-lipoxygenase is a cytosolic protein, whose amino acid sequence is 65% similar to human 5-lipoxygenase and 45% similar to type I soybean lipoxygenase (whose tridimensional structure has been resolved by... 

Lipoxygenase has been extensively studied with a purified preparation from rabbit reticulocytes [40,48]. In the course of reticulocyte maturation, the decline in 15-lipoxygenase appeared concomitantly with the breakdown of mitochondria, and mature erythrocytes have no 15-lipoxygenase [40]. In human tissues, eosinophils [134,135] and airway epithelial cells [78,136] are major sources... 

Lipoxygenase in homogenates from rat platelets [121] and human erythroleukaemia (HEL) cells [148] is translocated from the cytosol to membrane in a calcium-dependent manner. The calcium-dependent translocation has also been observed with rabbit reticulocyte 15-lipoxygenase [149]. 

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