Pc. Schmid et al., INCORPORATION OF EXOGENOUS FATTY-ACIDS INTO MOLECULAR-SPECIES OF RAT HEPATOCYTE PHOSPHATIDYLCHOLINE, Archives of biochemistry and biophysics, 322(2), 1995, pp. 306-312
Freshly isolated rat hepatocytes were incubated for 20 and 60 min with
[U-C-14]glycerol and unlabeled palmitic (16:0), oleic (18:1), or arac
hidonic (20:4) acid, added as albumin complex in 10% ethanol. Each fat
ty acid increased glycerol incorporation into total lipids by a factor
of 8-10 over control, whereas ethanol alone (final concentration 100
mM) yielded a threefold increase of glycerol uptake. Glycerol incorpor
ation stopped after 20 min and cellular acyl turnover continued in the
absence of useable labeled substrate, In each case, radioactivity rec
overed in hepatocyte lipids was present primarily in triacylglycerol (
37-64%), phosphatidylcholine (22-37%), and phosphatidylethanolamine (1
0-22%). Separation by high-performance liquid chromatography of the di
acylglycerol dinitrobenzoates derived from phosphatidylcholine showed
that the molecular species had drastically different labeling patterns
in the presence of the exogenous fatty acids, whereas the pattern obt
ained in the presence of ethanol alone was virtually the same as that
for the control incubations. The labeling patterns indicated that exog
enous fatty acids, including arachidonic acid, were incorporated into
phosphatidylcholine primarily by the de novo pathway yielding highly l
abeled species with the exogenous fatty acid esterified at both the sn
-1 and sn-2 positions of glycerol. After 20 min incubation with arachi
donic acid, the 20:4-20:4 phosphatidylcholine contained about one-half
of the [U-C-14]glycerol label recovered in this lipid class. The data
also showed that newly synthesized molecular species were extensively
remodeled within 1 h. (C) 1995 Academic Press, Inc.