Gg. Gadelhak et Dw. Stanleysamuelson, INCORPORATION OF POLYUNSATURATED FATTY-ACIDS INTO PHOSPHOLIPIDS OF HEMOCYTES FROM THE TOBACCO HORNWORM, MANDUCA-SEXTA, Insect biochemistry and molecular biology, 24(8), 1994, pp. 775-785
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.