Biosynthesis of very long chain monounsaturated fatty acids by subcellular fractions of developing seeds

Potential oilseed crops from the semiarid region of northeastern Brazil

The caatinga semi-arid ecosystem of northeastern Brazil is characterized by a dry, spiny and predominantly deciduous shrub/forest vegetation, and many species there are potential sources of renewable resources for the oleochemical industry. The present research determined the oil content and fatty acid profiles of seeds from eight caatinga species. Seed oils were extracted in a Soxhlet system, and their fatty acid content identified by GC-MS. Oil content varied between 20.2% in Tabebuia impetiginosa (Mart.) Standl. (Bignoniaceae) and 46.4% in Barnebya harleyi (W.R. Anderson & B. Gates) Malpighiaceae. Anemopaegma laeve DC. (Bignoniaceae) had the highest oleic acid content (63.4%), while high levels of linoleic acid were found in Banisteriopsis pubipetala (Juss.) Cuatrec. (42.8%) and B. harleyi (31.9%) (both Malpighiaceae). Palmitic acid was the major fatty acid (50%) in Hippocratea volubilis (L.) (Celastraceae). High levels of linoleic and linolenic acids were found in Croton adamantinus Mull. Arg. (Euphorbiaceae), averaging 44.2% and 45.2% respectively. Gadoleic acid in was the most abundant fatty acid in the oil produced by Serjania lethalis A. St. Hill. (Sapindaceae), averaging 69.6%. B. pubipetala, B. harleyi, C. adamantinus, and H. volubilis were identified as promising species for cultivation.

Solubilization and partial purification of constituents of acyl-CoA elongase from Lunaria annua

All the constituent enzymes of acyl-CoA elongase, i.e., beta-ketoacyl-CoA synthase, beta-ketoacyl-CoA reductase, beta-hydroxyacyl-CoA dehydrase and trans-2-enoyl-CoA reductase, have been solubilized from a 15,000 x g particulate fraction from developing seeds of honesty (Lunaria annua) using Triton X-100. All these activities were retained upon subsequent precipitation of the solubilized protein with polyethylene glycol and resuspension of the precipitate followed by ion exchange chromatography of the resulting protein on DEAE-cellulose. A 4.2-fold enrichment of the acyl-CoA elongase was thus obtained. Further chromatography of the DEAE fraction containing all the constituents of acyl-CoA elongase on Ultrogel yielded a major protein fraction exhibiting the activities of beta-ketoacyl-CoA synthase and beta-ketoacyl-CoA reductase only. Almost 30-fold purification of the beta-ketoacyl-CoA synthase was thus achieved. The beta-ketoacyl-CoA synthase was inhibited only at high concentrations of cerulenin, but at very low concentrations of iodoacetamide. Inhibition could be reduced by preincubation with thioesters, indicating that an enzyme thioester intermediate is involved in the condensation reaction of the acyl-CoA elongation.

Acyl-CoA elongase from a higher plant (Lunaria annua): metabolic intermediates of very-long-chain acyl-CoA products and substrate specificity

A particulate fraction (15,000 x g pellet) from developing seeds of honesty (Lunaria annua) was found to synthesize very-long-chain acyl-CoA thioesters in a manner similar to mammalian systems, i.e., via condensation of an acyl-CoA with malonyl-CoA yielding beta-ketoacyl-CoA, which is reduced to beta-hydroxyacyl-CoA, the latter dehydrated to trans-2-enoyl-CoA that is finally reduced to very-long-chain acyl-CoA. Reduced pyridine nucleotides (NADH/NADPH) are required for the reduction steps. In the absence of reduced pyridine nucleotides only the condensation reaction occurs. The acyl-CoA elongase does not exhibit any pronounced specificity for any of the saturated (14:0 to 20:0) or (n - 9)cis-monounsaturated (14:1 to 22:1) acyl-CoA substrates, although both the saturated and monounsaturated acyl-CoA substrates having chain lengths of C18 and C20 are elongated somewhat faster.