Journal of Lipid Research, Vol 27, 731-741, Copyright © 1986 by Lipid Research, Inc.
Localization of phosphatidylethanolamine in microsomal membranes and regulation of its distribution by the fatty acid composition
C Valtersson, L Filipsson and G Dallner
Rat liver microsomes were incubated with the monofunctional aminoreagent
fluorescamine. Although the probe easily penetrated the membranes, two
pools of phosphatidylethanolamine (PE) could be detected. The first pool
rapidly reacted with the probe and comprised 80% of the total PE. The
second pool exhibited a very slow interaction. The two pools showed
differences in fatty acid composition as well as in their sites of
attachment. In vivo labeling with ethanolamine, glycerol, and palmitic and
stearic acid resulted in a higher specific activity in the first pool after
1 hr; equilibration with the second pool took about 3 hr. No equilibration
between the pools could be detected under in vitro conditions. In vivo
incorporation of labeled fatty acids showed that palmitic and stearic acids
were mainly incorporated into phosphatidylethanolamine by de novo
synthesis, while linoleic and arachidonic acids were introduced through
deacylation- reacylation processes. Injection of liposomes consisting of
labeled synthetic phosphatidylethanolamines into the portal vein was
followed by uptake by the hepatocytes and incorporation of the lipids into
the microsomal membranes. Depending on the fatty acid composition of the
injected lipid, one of either of the two pools became labeled. It is
suggested that the fatty acid composition of a given phospholipid molecule
exerts a signal function directing the lipid to its final intramembranous
location.
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