Author/Authors :
Susanne Tornhamre، نويسنده , , Annika Elmqvist، نويسنده , , Jan ?ke Lindgren، نويسنده ,
Latin Abstract :
The unstable epoxide leukotriene (LT) A4 is a key intermediate in leukotriene biosynthesis, but may also be transformed to lipoxins via a second lipoxygenation at C-15. The capacity of various 12- and 15-lipoxygenases, including porcine leukocyte 12-lipoxygenase, a human recombinant platelet 12-lipoxygenase preparation, human platelet cytosolic fraction, rabbit reticulocyte 15-lipoxygenase, soybean 15-lipoxygenase and human eosinophil cytosolic fraction, to catalyze conversion of LTA4 to lipoxins was investigated and standardized against the ability of the enzymes to transform arachidonic acid to 12- or 15-hydroxyeicosatetraenoic acids (HETE), respectively. The highest ratio between the capacity to produce lipoxins and HETE (LX/HETE ratio) was obtained for porcine leukocyte 12-lipoxygenase with an LX/HETE ratio of 0.3. In addition, the human platelet 100 000×g supernatant 12-lipoxygenase preparation and the human platelet recombinant 12-lipoxygenase and human eosinophil 100 000×g supernatant 15-lipoxygenase preparation possessed considerable capacity to produce lipoxins (ratio 0.07, 0.01 and 0.02 respectively). In contrast, lipoxin formation by the rabbit reticulocyte and soybean 15-lipoxygenases was much less pronounced (LX/HETE ratios <0.002). Kinetic studies of the human lipoxygenases revealed lower apparent Km for LTA4 (9–27 μM), as compared to the other lipoxygenases tested (58–83 μM). The recombinant human 12-lipoxygenase demonstrated the lowest Km value for LTA4 (9 μM) whereas the porcine leukocyte 12-lipoxygenase had the highest Vmax. The profile of products was identical, irrespective of the lipoxygenase used. Thus, LXA4 and 6S-LXA4 together with the all-trans LXA4 and LXB4 isomers were isolated. Production of LXB4 was not observed with any of the lipoxygenases. The lipoxygenase inhibitor cinnamyl-3,4-dihydroxy-α-cyanocinnamate was considerably more efficient to inhibit conversion of LTA4 to lipoxins, as compared to the inhibitory effect on 12-HETE formation from arachidonic acid (IC50 1 and 50 μM, respectively) in the human platelet cytosolic fraction.
NaturalLanguageKeyword :
Lipoxygenation , Lipoxin synthesis , Leukotriene A4 , Eosinophil 15-lipoxygenase , Platelet 12-lipoxygenase
