Journal of Lipid Research, Vol 18, 239-245, Copyright © 1977 by Lipid Research, Inc.
Stimulation by serum of 32P incorporation into the phospholipids of Ehrlich ascites cells
PB Schneider
Ehrlich ascites cells adapted for suspension culture were incubated with
32PO43- in a Krebs-Ringer-HEPES (N-2-hydroxyethyl-piperazine-N'-2-
ethanesulfonate) buffer with or without 5% calf serum. Specific activity
was determined for cellular [gamma-32P]ATP, total phospholipids, and the
individual phospholipids fractionated by two- dimensional thin-layer
chromatography. Serum stimulated the incorporation of 32P into the
phosphatides with a 2-3-fold increase in specific activity of
phosphatidylcholine and phosphatidylethanolamine. Phosphatidylinositol
showed a moderate increase. Phosphatidic acid showed an increase that could
be accounted for by a parallel small increase in the specific activity of
precursor [gamma-32P]-ATP. The effect os serum could be discerned as early
as 10 min after its addition. Complete inhibition of protein synthesis by
cycloheximide or puromycin did not interfere with the serum stimulation of
32P incorporation into lipids, indicating that the serum effect is not
dependent on synthesis of new protein. Incubation with palmitic acid caused
a marked increase of phosphatidylinositol specific activity, little change
in specific activity of phosphatidic acid but a tripling of its total
amount, and no changes in the other phosphatides. Oleic acid caused only a
small increase in phosphatidylinositol specific activity and no significant
changes in the other lipids.
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