Conditions for the formation of the oxo derivatives of arachidonic acid from platelet 12-lipoxygenase and soybean 15-lipoxygenase.
Three carbonyl compounds derived from arachidonic acid have recently been characterized in human platelets, namely, 12-ketoeicosatetraenoic acid and two isomeric 12-oxododecatrienoic acids. The conditions for the synthesis of these compounds and for the synthesis of analogous products from soybean lipoxygenase, i.e., 15-ketoeicosatetraenoic acid and 15-oxopentadecatetraenoic acids, were compared with regard to the role of oxygen and fatty acid availability, and heme catalysis. Using platelet homogenates or soybean lipoxygenase and arachidonic acid as a substrate, it was found that the establishment of anaerobic conditions during the incubation was mandatory only for the synthesis of 15-oxopentadecatetraenoic acids. Anaerobic conditions, however, greatly increased the formation of 15-ketoeicosatetraenoic acid and, to a lesser extent, of 12-oxododecatrienoic acids. On the other hand, 12-hydroperoxyeicosatetraenoic acid (12-HPETE) was transformed into 12-ketoeicosatetraenoic acid and 12-oxododecatrienoic acids by platelet homogenates or soybean lipoxygenase. This transformation was increased when the incubation was performed in anaerobic conditions and in the presence of a fatty acid substrate of the enzyme. These data suggest that oxygen deprivation and excess fatty acid could play a stimulatory role in the synthesis of 12-oxo compounds by platelets. Finally, we have compared the heme-catalyzed generation of the 12-oxo and 15-oxo derivatives from their hydroperoxide precursors: whereas 12-oxododecatrienoic acids and 12-ketoeicosatetraenoic acid were formed in the proportion of 8.5: 1.5 from 12-HPETE incubated with hematin (150 nM), 15-ketoeicosatetraenoic acid was the only carbonyl compound generated from 15-HPETE in the same conditions, emphasizing the unique reactivity of the 12-HPETE.
D001092:Arachidonate 12-Lipoxygenase / Q000097:blood*; D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism*; D001091:Arachidonate Lipoxygenases / Q000097:blood* / Q000378:metabolism*; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D001792:Blood Platelets / Q000201:enzymology*; D005227:Fatty Acids / Q000494:pharmacology; D006427:Hemin / Q000378:metabolism; D006801:Humans; D015289:Leukotrienes; D008054:Lipid Peroxides / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D010944:Plants / Q000201:enzymology*; D013025:Glycine max
D001095:Arachidonic Acids; D005227:Fatty Acids; D015289:Leukotrienes; D008054:Lipid Peroxides; D016718:Arachidonic Acid; C021201:12-HPETE; C025086:15-hydroperoxy-5,8,11,13-eicosatetraenoic acid; D006427:Hemin; D001091:Arachidonate Lipoxygenases; D001092:Arachidonate 12-Lipoxygenase; D001093:Arachidonate 15-Lipoxygenase; D010100:Oxygen