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Influence of the cis-9, cis-12 and cis-15 double bond position in octadecenoic acid (18:1) isomers on the rat FADS2-catalyzed Delta 6-desaturation

Abstract : Oleic (cis9-18:1), linoleic (cis9,cis12-18:2) and alpha-linolenic (cis9,cis12,cis15-18:3) acids are well described substrates of the Delta 6-desaturase encoded by the mammalian fatty acid desaturase 2 (FADS2) gene. In addition, at least 9 other very structurally different fatty acids have been shown to be Delta 6- or even Delta 8-desaturated by the FADS2 protein. A better characterization of the substrate specificity of this enzyme is therefore needed. By using commercial cis9-18:1 and chemically synthesized cis12- and cis15-18:1 (sharing the n-6 double bond with 18:2 n-6 and the n-3 double bond with 18:3 n-3, respectively), we tried to decrypt the fatty acid structure driving the FADS2 substrate affinity. We first showed that both recombinant and native rat FADS2 were able to Delta 6-desaturate not only the cis9- but also the cis12- and cis15-18:1 isomers. Next, the inhibitory effect of increasing concentrations of each 18:1 isomer was investigated in vitro on the Delta 6-desaturation of a-linolenic acid. At equimolar inhibitor/substrate ratio (60 mu M), the cis9-18:1 exhibited a significantly higher inhibition (25%) than the cis12- (8%) and cis15-18:1 (5%). This study shows that a single cis double bond in 12- or 15-position in 18:1 is enough to make them low Delta 6-desaturable substrates. If a preexisting cis9-double bond is not absolutely required for the Delta 6-desaturation of octadecenoic acids, its presence is however crucial to explain the higher enzyme affinity. Compared with oleic acid, the additional presence of a cis12-double bond in linoleic acid increased its inhibitory effect on the Delta 6-desaturation of alpha-linolenic acid at low concentration (30 mu M) but not at higher concentrations (60 and 120 mu M). In this classification of the decreasing impact of the double bond when it comes closer to the methyl end of octadecenoic acids, the cis11-18:1 (cis-vaccenic acid) should be considered apart since it is itself not Delta 6-desaturated but still a good competitive inhibitor of the a-linolenic acid 6-desaturation. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
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Vincent V. Rioux, Benjamin Choque, Hélène Ezanno, Cécile Duby, Daniel D. Catheline, et al.. Influence of the cis-9, cis-12 and cis-15 double bond position in octadecenoic acid (18:1) isomers on the rat FADS2-catalyzed Delta 6-desaturation. Chemistry and Physics of Lipids, Elsevier, 2015, 187, pp.oct-19. ⟨10.1016/j.chemphyslip.2015.02.001⟩. ⟨hal-01409003⟩



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