Low C-18 to C-20 fatty acid elongase activity and limited conversion of stearidonic acid, 18 : 4(n-3), to eicosapentaenoic acid, 20 : 5(n-3), in a cell line from the turbot, Scophthalmus maximus

The TF cell line, derived from a top predatory, carnivorous marine teleost, the turbot (Scophthalmus maximus). is known to have a limited conversion o f C-18 to C-20 polyunsaturated fatty acids (PUFA). To illuminate the underl ying processes, we studied the conversions of stearidonic acid, 18:4(n-3), and its elongation product, 20:4(n 3), in TF cells and also in a cell line, AS, derived from Atlantic salmon (Salmo salar), by adding unlabelled (25 m u M), U-C-14 (1 mu M) or deuterated (d5; 25 mu M) fatty acids. Stearidonic acid, 18:4(n-3), was metabolised to 20:5(n-3) in both cells lines, but more so in AS than in TF cells. Delta 5 desaturation was more active in TF cell s than in AS cells, whereas C-18 to C-20 elongation was much reduced in TF as compared to AS cells. Only small amounts of docosahexaenoic acid (22:6(n -3)) were produced by both cell lines, although there was significant produ ction of 22:5(n-3) in both cultures. especially when 20:4(n-3) was suppleme nted. We conclude that limited elongation of C-18 to C-20 fatty acids rathe r than limited fatty acyl Delta 5 desaturation accounts for the limited rat e of conversion of 18:3(n-3) to 20:5(n-3) in the turbot cell line, as compa red to the Atlantic salmon cell line. The results can account for the known differences in conversions of C-18 to C-20 PUFA by the turbot and the Atla ntic salmon in vivo. (C) 1999 Elsevier Science B.V. All rights reserved.