Characterization of the trans 2–3 enoyl-CoA reductase of the acyl-CoA elongase from leek (Allium porrum L.)

The acyl-CoA elongase, responsible for the synthesis of very long chain fatty acids (VLCFA), has been purified from leek (1) Lunaria annua (2) and rapeseeds (3). In both cases the molecular mass of the Triton micelle containing the acyl-CoA elongase was estimated by gel filtration chromatography as about 300kDa. The SDS-Page electrophoresis analysis has shown the presence of 3 to 4 different proteins, having 59 to 65 kDa as molecular mass (1,2), strongly suggesting that the acyl-CoA could be a multienzyme complex. It was generally admitted that the elongation process involved the following reactions: condensation of the acyl-CoA to malonyl CoA to form a 3-ketoacyl-CoA, reduction of this 3-ketoacyl-CoA, dehydratation of the resulting 3-OH acyl-CoA and finally reduction of the trans 2–3 enoyl-CoA (4). An important point concerning the knowledge of the elongation mechanism and the structure of the acyl-CoA elongase is to determine the nature of the intermediate reaction catalyzed by each protein constituting the complex. The difficulty was the lack of acyl-CoAs susceptible to be the substrates of the intermediate reactions. The enoyl-CoA reductase from etiolated leek seedlings has been characterized using trans 2–3 C20-CoA synthesized chemically.