Characterization of an arachidonic acid-selective acyl-CoA synthetase from murine T lymphocytes.
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 competition studies using EL4 microsomes demonstrate that [14C]palmitoyl-CoA synthesis (Km = 13 +/- 1 microM, Vmax = 7 +/- 1 nmol/mg per min) is inhibited by unlabeled palmitate, oleate, linoleate or linolenate (Ki = 15-25 microM) and weakly by arachidonate (Ki greater than 100 microM). Similar inhibition is observed for the activation of [14C]oleate (Km = 31 +/- 3 microM, Vmax = 6 +/- 2 nmol/mg per min). On the other hand, [14C]arachidonyl-CoA synthetase (Km = 15 +/- 3 microM, Vmax = 13 +/- 2 nmol/mg per min) is inhibited by unlabeled arachidonic acid (Ki = 20 microM) 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 microM), 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.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D003065:Coenzyme A / Q000378:metabolism; D003066:Coenzyme A Ligases / Q000378:metabolism*; D005227:Fatty Acids / Q000494:pharmacology; D005228:Fatty Acids, Essential / Q000172:deficiency; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008861:Microsomes / Q000201:enzymology; D013379:Substrate Specificity; D013601:T-Lymphocytes / Q000201:enzymology*; D013602:T-Lymphocytes, Cytotoxic / Q000201:enzymology
D001095:Arachidonic Acids; D005227:Fatty Acids; D005228:Fatty Acids, Essential; D016718:Arachidonic Acid; D000255:Adenosine Triphosphate; D003066:Coenzyme A Ligases; D008274:Magnesium; D003065:Coenzyme A