Calcium/calmodulin-dependent conversion of 5-oxoeicosanoids to 6, 7-dihydro metabolites by a cytosolic olefin reductase in human neutrophils.
We previously showed that 6-trans isomers of leukotriene B4 but not leukotriene B4 itself are converted to dihydro metabolites by human neutrophils. The first step in the formation of these metabolites is oxidation of the 5-hydroxyl group by 5-hydroxyeicosanoid dehydrogenase. The objective of the present investigation was to characterize the second step in the formation of the dihydro metabolites, reduction of an olefinic double bond. We found that the olefin reductase reduces the 6,7-double bond of 5-oxoeicosanoids, is localized in the cytosolic fraction of neutrophils, and requires NADPH as a cofactor. Neutrophil cytosol converts a variety of both 5-oxo- and 15-oxoeicosanoids to dihydro products. However, conversion of 5-oxoeicosanoids to their 6,7-dihydro metabolites is inhibited by EGTA and a calmodulin antagonist and stimulated by the addition of calcium and calmodulin, whereas the reduction of 15-oxoeicosanoids to their 13,14-dihydro metabolites is slightly inhibited by calcium. Furthermore, eicosanoid Delta6- and Delta13-reductases could be separated by chromatography on DEAE-Sepharose. 5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is converted by the Delta6-reductase to 6,7-dihydro-5-oxo-ETE, which is 1000 times less potent than 5-oxo-ETE in mobilizing calcium in neutrophils. We conclude that neutrophils contain both 5-oxoeicosanoid Delta6-reductase and prostaglandin Delta13-reductase. Metabolism of 5-oxo-ETE by the Delta6-reductase results in loss of its biological activity.
Meakins-Christie Laboratories, Department of Medicine, McGill University, 3626 St. Urbain Street, Montreal, Quebec H2X 2P2, Canada.
K
K
Berhane
A A
AA
Ray
S P
SP
Khanapure
J
J
Rokach
W S
WS
Powell
D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000201:enzymology*; D015777:Eicosanoids / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009504:Neutrophils / Q000201:enzymology*; D010088:Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity
D002147:Calmodulin; D015777:Eicosanoids; D010088:Oxidoreductases; D002118:Calcium