Investigation of highly unsaturated fatty acid metabolism in the Asian sea bass, Lates calcarifer

Lates calcarifer, commonly known as the Asian sea bass or barramundi, is an interesting species that has great aquaculture potential in Asia including Malaysia and also Australia We have investigated essential fatty acid metabolism in this species, focusing on the endogenous highly unsaturated fatty acid (HUFA) synthesis pathway using both biochemical and molecular biological approaches Fatty acyl desaturase (Fad) and elongase (Elovl) cDNAs were cloned and functional characterization identified them as Delta 6 Fad and Elovl5 elongase enzymes, respectively The Delta 6 Fad was equally active toward 18 3n-3 and 18 2n-6, and Elovl5 exhibited elongation activity for C18-20 and C20-22 elongation and a trace of C22-24 activity The tissue profile of gene expression for Delta 6 fad and elovl5 genes, showed brain to have the highest expression of both genes compared to all other tissues The results of tissue fatty acid analysis showed that the brain contained more docosahexaenoic acid (DHA, 22 6n-3) than flesh, liver and intestine The HUFA synthesis activity in Isolated hepatocytes and enterocytes using [1-C-14]18 3n-3 as substrate was very low with the only desaturated product detected being 18 4n-3 These findings indicate that L calcarifer display an essential fatty acid pattern similar to other marine fish in that they appear unable to synthesize HUFA from C-18 substrates High expression of Delta 6 fad and elovl5 genes in brain may indicate a role for these enzymes in maintaining high DHA levels in neural tissues through conversion of 20 5n-3