INCORPORATION OF POLYUNSATURATED FATTY-ACIDS INTO PHOSPHOLIPIDS OF HEMOCYTES FROM THE TOBACCO HORNWORM, MANDUCA-SEXTA

We examined the incorporation of four radioactive fatty acids, 18:1n-9 , 18:2n-6, 20:4n-6 and 20:5n-3, into cellular lipids of hemocytes from tobacco hornworms, Manduca sexta. Most of the radioactivity associate d with 18:1n-9 was recovered from triacylglcyerols (TGs), and the radi oactivity associated with 18:2n-6 was heavily incorporated into phosph olipids (PLs) and TGs. Most of the radioactivity associated with the t wo eicosanoid-precursor polyunsaturated fatty acids (PUFAs), 20:4n-6 a nd 20:5n-3, was incorporated into PLs. The incorporated fatty acids we re redistributed among the lipid classes during 20 incubations. The tw o C20 PUFAs were moved from PLs to TGs. While 18:2n-6 underwent little change, 18:1n-9 was redistributed from TGs to PLs. Within PLs, each o f the fatty acids were incorporated into phosphatidylcholine (PC), pho sphatidylethanolamine (PE), phosphatidylglycerol (PtG) and phosphatidy lserine/inositol (PS/PI). The incorporation patterns changed over time , indicating that the incorporated fatty acids were redistributed amon g the four PL fractions. The radioactivity associated with 18:1n-9 was mostly recovered from the sn-1 position of PC (59%) and PE (83%). Mos t of the radioactivity associated with 18:2n-6 was found in the sn-2 p osition of PC (88%) and PE (67%). Over 90% of the radioactivity associ ated with 20:5n-3 was recovered from the sn-2 position of PC and PE. I ncorporation of 20:4n-6 differed from 20:5n-3 because more radioactivi ty was recovered from the sn-2 position of PC (93%) than PE (69%). The se findings are in line with the general background of lipid biochemis try, from which incorporation of 20:4n-6 into PE marks a notable depar ture: 31% of the radioactivity associated with this acid was recovered from the sn-1 position of PE. These findings indicate that hemocytes from the tobacco hornworm elaborate a fatty acid incorporation system, which exhibits specificity with respect to fatty acid structure and l ipid class.