Fatty acid chain elongation synthesis in eel (Anguilla anguilla) liver mitochondria

The properties of fatty acid chain elongation synthesis have been investigated in liver mitochondria of the European eel (Anguilla anguilla). The incorporation of [1-(14)C]acetyl-CoA into fatty acids shows a specific activity of 0.43+/-0.05 nmol/min x mg protein (n=6), which is more than twice higher than that previously reported in rat liver mitochondria. Label incorporation into fatty acids was, in mitochondria disrupted by freezing and thawing, much higher than in intact organelles thus suggesting a probable localization of this pathway inside mitochondria. Only a negligible acetyl-CoA incorporation into fatty acids occurs in the absence of ATP, Mg2+ or reduced pyridine nucleotides; NADH alone seems to be as effective as NADH + NADPH as a hydrogen donor for the reducing steps. CoASH, without effect up to 10 microM, showed a strong inhibition at higher concentrations. From the ratio of total radioactivity and radioactivity in carboxyl carbon it can be inferred that in eel-liver mitochondria only chain elongation of preexisting fatty acids occurs. A significant fatty acid chain elongation activity is also present when, instead of acetyl-CoA, [2-(14)C]malonyl-CoA is used as a carbon unit donor. Moreover, the synthesized fatty acids were actively incorporated into phopholipids, mainly phosphatidylcholine, phosphatidylethanolamine and sphyngomyelin.