Characterization and solubilization of an acyl chain elongation system in microsomes of leek epidermal cells.

Microsomes prepared from leek epidermal tissue readily elongate stearoyl-CoA to very long chain fatty acid with malonyl-CoA as the C2 unit. In the absence of stearoyl-CoA, but in the presence of ATP, microsomes elongate endogenous free fatty acids. Endogenous CoA is the source of CoA. Palmitoyl, stearoyl, and higher saturated acyl-CoAs are readily elongated by the microsomal system but oleoyl-CoA is ineffective; however, the higher monounsaturated acyl-CoAs can be elongated. Since the very long chain fatty acids of the leek epidermis are all saturated, it would appear that the reaction controlling the nature of the final acyl product is the inactivity of oleoyl-CoA as a substrate. There is no evidence that acyl carrier protein participates in the elongation reactions. Evidence is also presented suggesting that (a) there may be two elongation systems, one responsible for the conversion of stearoyl-CoA to arachidonyl-CoA and the second involved in the conversion of arachidonyl-CoA to very long chain fatty acids, and that (b) the elongation activities may be associated with a large polypeptide.