Cloning and nutritional regulation of a Delta6-desaturase-like enzyme in the marine teleost gilthead seabream (Sparus aurata).

Marine fish are presumed to have a lower capacity than freshwater fish for the bioconvertion of 18C fatty acids into 20-22C highly unsaturated fatty acids (HUFA). The present work investigated the first step of this pathway, the Delta6-desaturation, in gilthead seabream. A full-length desaturase-like cDNA was identified from total RNA extracted from viscera of juvenile fish fed for 96 days on an experimental HUFA-free diet containing olive oil as the sole lipid source. The open reading frame encodes a 445-amino acid peptide that contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b(5) domain, which are characteristic of Delta6- and Delta5-desaturases. Predicted protein sequence of seabream desaturase-like indicated a high percentage of identity with mammalian Delta6-desaturases (approx. 65%). Northern analysis showed two transcripts of approximately 3.7 and 1.8 kb which were highly expressed in fish fed on HUFA-free diet and slightly expressed in fish fed on HUFA-rich diet. The fatty acid profile of the former group was characterized by high levels of Delta6-desaturation products (18:2 n-9 and 20:2 n-9) with no detectable levels of Delta5-desaturation product (20:3n-9). These results demonstrate for the first time the presence and nutritional modulation of a Delta6-desaturase-like cDNA in a marine fish.