Glycerophospholipid
Glycerophospholipids or phosphoglycerides are
Structures
Glycerophospholipids are derived from
They are usually organized into a bilayer in membranes with the polar hydrophilic heads sticking outwards to the aqueous environment and the non-polar hydrophobic tails pointing inwards.[6] Glycerophospholipids consist of various diverse species which usually differ slightly in structure. The most basic structure is a phosphatidate. This species is an important intermediate in the synthesis of many phosphoglycerides. The presence of an additional group attached to the phosphate allows for many different phosphoglycerides.
By convention, structures of these compounds show the 3 glycerol carbon atoms vertically with the phosphate attached to carbon atom number three (at the bottom). Plasmalogens and phosphatidates are examples.[7]
Nomenclature and stereochemistry
In general, glycerophospholipids use an "sn" notation, which stands for
The advantage of this particular notation is that the spatial configuration (D or L) of the glycero-molecule is determined intuitively by the residues on the positions sn-1 and sn-3.
For example sn-glycero-3-phosphoric acid and sn-glycero-1-phosphoric acid are enantiomers.
Most vegetable oils have unsaturated fatty acids in the sn-2 position, with saturated fatty acids in the 1-sn and/or 3-sn position.[8] Animal fats more often have saturated fatty acids in the 2-sn, with unsaturated fatty acids in the 1-sn and/or 3-sn position.[8]
Examples
- Plasmalogens
Plasmalogens are a type of phosphoglyceride. The first carbon of glycerol has a hydrocarbon chain attached via an ether, not ester, linkage. The linkages are more resistant to chemical attack than ester linkages are. The second (central) carbon atom has a fatty acid linked by an ester. The third carbon links to an ethanolamine or choline by means of a phosphate ester. These compounds are key components of the membranes of muscles and nerves.
- Phosphatidates
Phosphatidylethanolamines, phosphatidylcholines, and other phospholipids are examples of phosphatidates.
- Phosphatidylcholines
Phosphatidylcholines are lecithins. Choline is the alcohol, with a positively charged quaternary ammonium, bound to the phosphate, with a negative charge. Lecithins are present in all living organisms. An egg yolk has a high concentration of lecithins, which are commercially important as an emulsifying agent in products such as mayonnaise. Lecithins are also present in brain and nerve tissue.
- Phosphatidylinositol
Phosphatidylinositol makes up a small component of the cytosol in eukaryotic cell membranes and gives molecules a negative charge. Its importance relies in its role in activating sensory receptors that correlate with taste functions.
- Phosphatidylserine
Phosphatidylserine is important in cell signaling, specifically apoptosis. Cells will use this phosphatidylserine to enter cells via apoptotic mimicry. The structure of this lipid differs in plants and animals, regarding fatty acid composition. In addition, phosphatidylserine plays an important role in the human brain content, as it makes up 13–15% of the phospholipids in the human cerebral cortex. This lipid is found in a wide range of places. For example, in the human diet, about 130 mg are derived from phosphatidylserine. This has been said to have a positive impact on the brain, as it helps with reduced stress and improved memory.[10]
- Sphingomyelin
- Other phospholipids
There are many other phospholipids, some of which are
Uses
Functions and use in membranes
Glycerophospholipids are the main structural component of biological membranes. Their amphipathic nature drives the formation of the lipid bilayer structure of membranes. The cell membrane seen under the electron microscope consists of two identifiable layers, or "leaflets", each of which is made up of an ordered row of glycerophospholipid molecules. The composition of each layer can vary widely depending on the type of cell.
- For example, in human plasma membrane consists mainly of phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol.
- By contrast, the exoplasmic side (the side on the exterior of the cell) consists mainly of phosphatidylcholine and sphingomyelin, a type of sphingolipid.
Each glycerophospholipid molecule consists of a small
- the hydrophobictails point to each other and form a fatty, hydrophobic center
- the ionichead groups are placed at the inner and outer surfaces of the cell membrane
Apart from their function in cell membranes, they function in other cellular processes such as signal induction and transport. In regards to signaling, they provide the precursors for prostanglandins and other leukotrienes.[12] It is their specific distribution and catabolism that enables them carry out the biological response processes listed above.[13] Their roles as storage centers for secondary messengers in the membrane is also a contributing factor to their ability to act as transporters.[13] They also influence protein function. For example, they are important constituents of lipoproteins (soluble proteins that transport fat in the blood) hence affect their metabolism and function.[6]
Use in emulsification
Glycerophospholipids can also act as an
Presence in the brain
Neural membranes contain several classes of glycerophospholipids which turnover at different rates with respect to their structure and localization in different cells and membranes. There are three major classes namely; 1-alkyl-2-acyl glycerophospholipid, 1,2-diacyl glycerophospholipid and plasmalogen. The main function of these classes of glycerophospholipids in the neural membranes is to provide stability, permeability and fluidity through specific alterations in their compositions.
Metabolism
The metabolism of glycerophospholipids is different in eukaryotes, tumor cells,[15] and prokaryotes. Synthesis in prokaryotes involves the synthesis of glycerophospholipids phosphatidic acid and polar head groups. Phosphatidic acid synthesis in eukaryotes is different, there are two routes, one to the other toward phosphatidylcholine and phosphatidylethanolamine. Glycerophospholipids are generally metabolized in several steps with different intermediates. The very first step in this metabolism involves the addition or transfer of the fatty acid chains to the glycerol backbone to form the first intermediate, lysophosphatidic acid (LPA). LPA then becomes acylated to form the next intermediate phosphatidic acid (PA). PA can be dephosphorylated leading to the formation of diacylglycerol which is essential in the synthesis of phosphatidylcholine (PC).[6] PC is one of the many species of glycerophospholipids. In a pathway called the Kennedy pathway, the polar heads are added to complete the formation of the entire structure consisting of the polar head regions, the two fatty acid chains and the phosphate group attached to the glycerol backbone. In this Kennedy pathway, Choline is converted to CDP-Choline which drives the transfer of the polar head groups to complete the formation of PC. PC can then be further converted to other species of glycerophospholipids such as phosphatidylserine (PS) and phosphatidylethanolamine (PE).[6]
See also
References
- ISSN 1471-0080.
- ^ PMID 28007654.
- PMID 24646950.
- S2CID 205804071.
- ^ PMID 24462586.
- PMID 18369234.
- ^ PMID 29301208.
- ^ Moss G.P. (www version) (1976). "Nomenclature of Lipids, Recommendations 1976". IUPAC-IUB Commission on Biochemical Nomenclature (CBN). Part I. Fatty Acid, Neutral Fats, Long-Chain Alcohols and Long-Chain Bases § Lip-1.13. Retrieved 27 Sep 2023.
- ^ "Scientific Opinion on the substantiation of health claims related to phosphatidyl serine (ID 552, 711, 734, 1632, 1927) pursuant to Article 13(1) of Regulation (EC) No 1924/2006 | EFSA". www.efsa.europa.eu. 2010-10-19. Retrieved 2023-11-29.
- ISSN 0968-0004.
- PMID 21382416.
- ^ PMID 10878232.
- ^ Garcia, Christina (2011-06-30). "Metabolism of glycerophospholipids". We Sapiens.org. Archived from the original on 2012-03-23.
- PMID 21222647.
External links
- Glycerophospholipids at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Diagram at uca.edu