Phosphatidylethanolamines are found in all living cells, composing 25% of all phospholipids. In human physiology, they are found particularly in nervous tissue such as the
white matter of
brain, nerves, neural tissue, and in
spinal cord, where they make up 45% of all phospholipids.[2]
As a polar head group, phosphatidylethanolamine creates a more viscous lipid membrane compared to
phosphatidylcholine. For example, the melting temperature of di-oleoyl-phosphatidylethanolamine is -16 °C while the melting temperature of di-oleoyl-phosphatidylcholine is -20 °C. If the lipids had two palmitoyl chains, phosphatidylethanolamine would melt at 63 °C while phosphatidylcholine would melt already at 41 °C.[4] Lower melting temperatures correspond, in a simplistic view, to more fluid membranes.
In humans
In humans, metabolism of phosphatidylethanolamine is thought to be important in the heart. When blood flow to the heart is restricted, the asymmetrical distribution of phosphatidylethanolamine between membrane leaflets is disrupted, and as a result the membrane is disrupted. Additionally, phosphatidylethanolamine plays a role in the secretion of
lipoproteins in the liver. This is because vesicles for secretion of
very low-density lipoproteins coming off of the
Golgi apparatus have a significantly higher phosphatidylethanolamine concentration when compared to other vesicles containing very low-density lipoproteins.[5] Phosphatidylethanolamine has also shown to be able to propagate infectious
prions without the assistance of any
proteins or
nucleic acids, which is a unique characteristic of it.[6] Phosphatidylethanolamine is also thought to play a role in blood clotting, as it works with
phosphatidylserine to increase the rate of
thrombin formation by promoting binding to
factor V and
factor X, two proteins which catalyze the formation of thrombin from
prothrombin.[7] The synthesis of endocannabinoid
anandamide is performed from the phosphatidylethanolamine by the successive action of 2 enzymes, the N-
acetyltransferase and
phospholipase-D.[8]
In bacteria
Where phosphatidylcholine is the principal
phospholipid in animals, phosphatidylethanolamine is the principal one in
bacteria. One of the primary roles for phosphatidylethanolamine in bacterial membranes is to spread out the negative charge caused by
anionic membrane
phospholipids. In the bacterium E. coli, phosphatidylethanolamine play a role in supporting
lactose permeases active transport of lactose into the cell, and may play a role in other transport systems as well. Phosphatidylethanolamine plays a role in the assembly of lactose permease and other membrane proteins. It acts as a 'chaperone' to help the membrane proteins correctly fold their
tertiary structures so that they can function properly. When phosphatidylethanolamine is not present, the transport proteins have incorrect tertiary structures and do not function correctly.[9]
Phosphatidylethanolamine also enables bacterial multidrug transporters to function properly and allows the formation of intermediates that are needed for the transporters to properly open and close.[10]
Structure
As a
lecithin, phosphatidylethanolamine consists of a combination of
glycerol esterified with two
fatty acids and
phosphoric acid. Whereas the phosphate group is combined with
choline in phosphatidylcholine, it is combined with
ethanolamine in phosphatidylethanolamine. The two fatty acids may be identical or different, and are usually found in positions 1,2 (less commonly in positions 1,3).
Synthesis
The
phosphatidylserinedecarboxylation pathway and the
cytidine diphosphate-ethanolamine pathways are used to synthesize phosphatidylethanolamine.
Phosphatidylserine decarboxylase is the enzyme that is used to decarboxylate phosphatidylserine in the first pathway. The phosphatidylserine decarboxylation pathway is the main source of synthesis for phosphatidylethanolamine in the membranes of the
mitochondria. Phosphatidylethanolamine produced in the mitochondrial membrane is also transported throughout the cell to other membranes for use. In a process that mirrors
phosphatidylcholine synthesis, phosphatidylethanolamine is also made via the cytidine diphosphate-ethanolamine pathway, using
ethanolamine as the substrate. Through several steps taking place in both the
cytosol and
endoplasmic reticulum, the synthesis pathway yields the end product of phosphatidylethanolamine.[11] Phosphatidylethanolamine is also found abundantly in soy or egg lecithin and is produced commercially using chromatographic separation.
Regulation
Synthesis of phosphatidylethanolamine through the
phosphatidylserinedecarboxylation pathway occurs rapidly in the
inner mitochondrial membrane. However, phosphatidylserine is made in the
endoplasmic reticulum. Because of this, the transport of phosphatidylserine from the endoplasmic reticulum to the mitochondrial membrane and then to the inner mitochondrial membrane limits the rate of synthesis via this pathway. The mechanism for this transport is currently unknown but may play a role in the regulation of the rate of synthesis in this pathway.[12]
Presence in food, health issues
Phosphatidylethanolamines in food break down to form phosphatidylethanolamine-linked
Amadori products as a part of the
Maillard reaction.[13] These products accelerate
membranelipidperoxidation, causing
oxidative stress to cells that come in contact with them.[14] Oxidative stress is known to cause food deterioration and several diseases. Significant levels of Amadori-phosphatidylethanolamine products have been found in a wide variety of foods such as
chocolate,
soybean milk,
infant formula, and other
processed foods. The levels of Amadori-phosphatidylethanolamine products are higher in foods with high lipid and sugar concentrations that have high temperatures in processing.[13] Additional studies have found that Amadori-phosphatidylethanolamine may play a role in
vascular disease,[15] act as the mechanism by which
diabetes can increase the incidence of
cancer,[16] and potentially play a role in other diseases as well. Amadori-phosphatidylethanolamine has a higher
plasmaconcentration in diabetes patients than healthy people, indicating it may play a role in the development of the disease or be a product of the disease.[17]
^Wellner, Niels; Diep, Thi Ai; Janfelt, Christian; Hansen, Harald Severin (2012). "N-acylation of phosphatidylethanolamine and its biological functions in mammals". Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids. 1831 (3): 652–62.
doi:
10.1016/j.bbalip.2012.08.019.
PMID23000428.
^
abVance, Jean E.; Tasseva, Guergana (2012). "Formation and function of phosphatidylserine and phosphatidylethanolamine in mammalian cells". Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids. 1831 (3): 543–54.
doi:
10.1016/j.bbalip.2012.08.016.
PMID22960354.