title: Δ-6 Desaturase substrate competition: dietary linoleic acid (18:2n-6) has only trivial effects on α-linolenic acid (18:3n-3) bioconversion in the teleost rainbow trout.
abstract: It is generally accepted that, in vertebrates, omega-3 (n-3) and omega-6 (n-6) poly-unsaturated fatty acids (PUFA) compete for Δ-6 desaturase enzyme in order to be bioconverted into long-chain PUFA (LC-PUFA). However, recent studies into teleost fatty acid metabolism suggest that these metabolic processes may not conform entirely to what has been previously observed in mammals and other animal models. Recent work on rainbow trout has led us to question specifically if linoleic acid (LA, 18∶2n-6) and α-linolenic acid (ALA, 18∶3n-3) (Δ-6 desaturase substrates) are in direct competition for access to Δ-6 desaturase. Two experimental diets were formulated with fixed levels of ALA, while LA levels were varied (high and low) to examine if increased availability of LA would result in decreased bioconversion of ALA to its LC-PUFA products through substrate competition. No significant difference in ALA metabolism towards n-3 LC-PUFA was exhibited between diets while significant differences were observed in LA metabolism towards n-6 LC-PUFA. These results are evidence for minor if any competition between substrates for Δ-6 desaturase, suggesting that, paradoxically, the activity of Δ-6 desaturase on n-3 and n-6 substrates is independent. These results call for a paradigm shift in the way we approach teleost fatty acid metabolism. The findings are also important with regard to diet formulation in the aquaculture industry as they indicate that there should be no concern for possible substrate competition between 18∶3n-3 and 18∶2n-6, when aiming at increased n-3 LC-PUFA bioconversion in vivo.
authors: School of Life and Environmental Sciences, Deakin University, Warrnambool, Victoria, Australia.
authors: James A
authors: JA
authors: Emery
authors: Karen
authors: K
authors: Hermon
authors: Noor K A
authors: NK
authors: Hamid
authors: John A
authors: JA
authors: Donald
authors: Giovanni M
authors: GM
authors: Turchini
mesh_terms: D000818:Animals; D004032:Diet; D005247:Feeding Behavior / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D019787:Linoleic Acid / Q000494:pharmacology*; D050602:Linoleoyl-CoA Desaturase / Q000235:genetics / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D013379:Substrate Specificity / Q000187:drug effects; D017962:alpha-Linolenic Acid / Q000494:pharmacology*
chemical_list: D017962:alpha-Linolenic Acid; D019787:Linoleic Acid; D050602:Linoleoyl-CoA Desaturase