Evidence is presented that the murine thymoma EL4 and cytotoxic T lymphocyte clones possess two distinct long-chain fatty acyl-CoA synthetase activities. One enzyme shows activity toward a broad spectrum of fatty acid substrates, similar to the long-chain fatty acyl-CoA synthetase from rat liver. The other enzyme is selective for arachidonic acid and related fatty acids. Fatty acid competetion studies using EL4 microsomes demonstrate that [14C]palmitoyl-CoA synthesis (Km = 13 ± 1 μM, Vmax = 7 ± 1 nmol/mg per min) is inhibited by unlabeled palmitate, oleate, linoleate or linolenate (Ki = 15-25 μM) and weakly by arachidonate (Ki > 100 μM). Similar inhibition is observed for the activation of [14C]oleate (Km = 31 ± 3 μM, Vmax = 6 ± 2 nmol/mg per min). On the other hand, [14C]arachidonyl-CoA synthetase (Km = 15 ± 3 μM, Vmax = 13 ± 2 nmol/mg per min) is inhibited by unlabeled arachidonic acid (ki = 20 μM) but not by unlabeled palmitate, oleate, linoleate and linolenate. The description of arachidonoyl-CoA synthetase in cytotoxic T lymphocyte clones represents the first example of a cell with little or no capacity to synthesize arachidonic acid metabolites, yet which possesses a selective esterification mechanism for the fatty acid. Studies on the specificity of the arachidonic acid-selective acyl-CoA synthetase utilized arachidonic acid metabolites and structurally related fatty acids and yielded two points of interest: (1) metabolism of arachidonic acid to monohydroxy fatty acids (HETEs) resulted in compounds with significantly decreased ability to be activated by the arachidonate-selective acyl-CoA synthetase; (2) arachidonate was a much better substrate than was 5,8,11-eicosatrienoic acid (Km = 41 μM), the fatty acid which accumulates during essential fatty acid deficiency. The possible role of an arachidonic acid-selective acyl-CoA synthetase in lymphocyte activation and as a homeostatic mechanism during essential fatty acid deficiency is discussed.
|Number of pages||10|
|Journal||Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism|
|State||Published - Feb 8 1985|
- Acyl-CoA synthetase
- Essential fatty acid deficiency
- Lymphocyte activation