Phosphatidylcholine Dr. Narendhirakannan RT Assistant Professor Department of Biochemistry Phosphatidylcholine Phospholipids contain fatty acids, glycerol, and phosphorous. The phosphorous part of the phospholipid substance — the lecithin — is made up of PC. For this reason, the terms phosphatidylcholine and lecithin are often used interchangeably, although they're different. • Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup. • They are a major component of biological membranes and can be easily obtained from a variety of readily available sources, such as egg yolk or soybeans, from which they are mechanically or chemically extracted using hexane. • They are also a member of the lecithin group of yellow-brownish fatty substances occurring in animal and plant tissues. Dipalmitoyl phosphatidylcholine (a.k.a. lecithin) is a major component of pulmonary surfactant and is often used in the L/S ratio to calculate fetal lung maturity. • While phosphatidylcholines are found in all plant and animal cells, they are absent in the membranes of most bacteria • Phosphatidylcholine is a major constituent of cell membranes and pulmonary surfactant, and is more commonly found in the exoplasmic or outer leaflet of a cell membrane. • It is thought to be transported between membranes within the cell by phosphatidylcholine transfer protein (PCTP). • The body makes a brain chemical called acetylcholine from phosphatidylcholine. • Acetylcholine is important for memory and other bodily functions. • Since phosphatidylcholine might increase acetylcholine, there is interest in using it for improving memory and for conditions such as Alzheimer's disease. 1. It can help boost cognitive function 2. It may aid in liver repair 3. It may help protect against medication side effects 4. It may help ease symptoms of ulcerative colitis 5. It may promote lipolysis 6. It may help dissolve gallstones • PC helps support many of your body’s functions, ranging from fat metabolism to maintaining cell structure. You can get enough from foods such as eggs, red meat, and whole grains, and food sources are the best first choice Phosphatidyl ethanolamine • Phosphatidylethanolamines are a class of phospholipids found in biological membranes. • They are synthesized by the addition of cytidine diphosphate- ethanolamine to diglycerides, releasing cytidine monophosphate. • S-Adenosyl methionine can subsequently methylate the amine of phosphatidylethanolamines to yield phosphatidylcholines. • It can mainly be found in the inner (cytoplasmic) leaflet of the lipid bilayer • Phosphatidylethanolamine or 1,2-diacyl-sn-glycero-3- phosphoethanolamine (once given the trivial name 'cephalin') is usually the second most abundant phospholipid in animal and plant lipids, after phosphatidylcholine, and it is frequently the main lipid component of microbial membranes. • It can amount to 20% of liver phospholipids and as much as 45% of those of brain; higher proportions are found in mitochondria than in other organelles. • As such, it is obviously a key building block of membrane bilayers, and it is present exclusively in the inner leaflet of the plasma membrane, for example. • It is a neutral or zwitterionic phospholipid (at least in the pH range 2 to 7) • 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 • Phosphatidylethanolamines play a role in membrane fusion and in disassembly of the contractile ring during cytokinesis in cell division. • Additionally, it is thought that phosphatidylethanolamine regulates membrane curvature. • Phosphatidylethanolamine is an important precursor, substrate, or donor in several biological pathways • 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 have a significantly higher phosphatidylethanolamine concentration when compared to other vesicles containing very low-density lipoproteins Phosphatidylserine • Phosphatidylserine is a fatty substance called a phospholipid. • It covers and protects the cells in your brain and carries messages between them. • Phosphatidylserine plays an important role in keeping your mind and memory sharp. • Animal studies suggest that the level of this substance in the brain decreases with age. • Phosphatidylserine is used for Alzheimer's disease, age-related decline in mental function, improving thinking skills in young people, attention deficit-hyperactivity disorder (ADHD), depression, preventing exercise-induced stress, and improving athletic performance. • Although phosphatidylserine is distributed widely among animals, plants and microorganisms, it is usually less than 10% of the total phospholipids, the greatest concentration being in myelin from brain tissue. • For example, mouse brain and liver contain 14 and 3% phosphatidylserine, respectively. • However, it may comprise 10 to 20 mol% of the total phospholipids in the plasma membrane, where under normal conditions it is concentrated in the inner leaflet, and in the endoplasmic reticulum of cells. • In the yeast S. cerevisiae, it is a minor component of most cellular organelles other than the plasma membrane, where surprisingly it can amount to more than 30% of the total lipids. • In most bacteria, it is a minor membrane constituent, although it is important as an intermediate in phosphatidylethanolamine biosynthesis. • Membrane location: Phosphatidylserine modulates membrane charge locally, enabling the recruitment of soluble cations and proteins, and so it contributes to the organization of processes within cell membranes. • Its distribution within membranes is tightly controlled as it facilitates signalling within the various cellular compartments. • Enzyme activation: In addition to its function as a component of cellular membranes and as a precursor for other phospholipids, phosphatidylserine is an essential cofactor that binds to and activates a large number of proteins, especially those with signalling activities. • The negative charge on the lipid facilitates the binding to proteins through electrostatic interactions or Ca2+ bridges. • Blood coagulation: Phosphatidylserine is an important element of the blood coagulation process in platelets, where it is transported from the inner to the outer surface of the plasma membrane in platelets activated by exposure to fibrin-binding receptors. • Apoptosis: In addition in response to particular calcium-dependent stimuli, phosphatidylserine is known to have an important role in the regulation of apoptosis or programmed cell death, the natural process by which aged or damaged cells are removed from tissues before they can exert harmful effects. Phosphatidylinositol • Phosphatidylinositol consists of a family of lipids as illustrated on the right, a class of the phosphatidylglycerides. • In such molecules the isomer of the inositol group is assumed to be the myo- conformer unless otherwise stated. • Typically phosphatidylinositols form a minor component on the cytosolic side of eukaryotic cell membranes. • The phosphate group gives the molecules a negative charge at physiological pH. • The distinctive subcellular location of the different phosphoinositide species, together with the rapid and reversible nature of phosphorylation, gives them a central and general position in the fields of cell signalling cascades and intracellular membrane trafficking. • Phosphatidylinositol 4-phosphate is the precursor for the 4,5- bisphosphate, but it binds to a protein on the cytoskeleton of the cell and has its own characteristic functions. • It is the most widely distributed of the phosphoinositides, and in addition to the Golgi and the plasma membrane, it is present in late endosome, lysosomes, secretory vesicles and autophagosomes. Sphingomyelin • Sphingomyelin or ceramide 1-phosphocholine consists of a ceramide unit with a phosphorylcholine moiety attached to position 1 of the sphingoid base component. It is thus the sphingolipid analogue of phosphatidylcholine, and like that lipid it is zwitterionic. • Sphingomyelin is primarily of animal origin and is a ubiquitous component of all animal cell membranes, from mammals to nematodes (and in a few protozoa), where it is by far the most abundant sphingolipid. • Indeed, it can comprise as much as 50% or more of the lipids in certain tissues, though it is usually lower in concentration than phosphatidylcholine. • For example, it makes up about 10% of the lipids of brain, where it is a key constituent of myelin, but 70% of the phospholipids of the human lens. • Sphingomyelin is primarily of animal origin and is a ubiquitous component of all animal cell membranes, from mammals to nematodes (and in a few protozoa), where it is by far the most abundant sphingolipid. • Indeed, it can comprise as much as 50% or more of the lipids in certain tissues, though it is usually lower in concentration than phosphatidylcholine. • For example, it makes up about 10% of the lipids of brain, where it is a key