Fatty acid metabolism by a particulate fraction from germinating peas

The incorporation of fatty acids into lipid fractions was studied using a high-speed particulate fraction from germinating peas (Pisum sativum cv Feltham First). The acids were incorporated principally into the acyl-CoA and polar lipid fractions, with unsaturated fatty acids labelling the latter fraction at higher rates than saturated substrates. α-Hydroxylation also occurred. Oleate from oleoyl-CoA or oleoyl-acyl carrier protein was incorporated into polar lipids faster than from ammonium oleate. The incorporation of fatty acids into polar lipids was dependent on the presence of CoA and ATP in the medium and on the consequent generation of acyl-CoA's. Time-course studies and experiments when two fatty acid substrates were added consecutively confirmed the role of acyl-CoA's in the transfer of acyl groups to phospholipids. Although CoA was necessary when acyl-CoA's had to be generated, high concentrations were found to inhibit the rate ofacyl transfer. The results are discussed in terms ofthe ‘witching mechanism’ for controlling the fate of fatty acids in the plant cell.