by Denise McKee, Ph.D.
There are five general classes of phospholipids. These are phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylsphingomyelin.The structures and functions of the classes vary, but each starts with the same basic configuration.The special characteristics of the different classes of phospholipids depend upon which element is attached,at the head i.e., whether serine, choline, inositol or ethanolamine is attached, although it is now beginning to be realized that the activity of these phospholipids may also be influenced by which fatty acids make up the tails.
Phosphatidylcholine is an excellent source of choline, a B vitamin. Phosphatidylcholine is the major component of cell membranes and is critical for brain and liver function. In the brain, phosphatidylcholine is the precursor to acetylcholine. In digestion, phosphatidylcholine is part of the bile complex that emulsifies fats to facilitate absorption. Technically, phosphatidylcholine is lecithin, although the term is now used more frequently for the mixed phospholipid byproducts of seed oil refining.
Phosphatidylethanolamine is usually the second most abundant phospholipid in animal and plant lipids and is a key building block of cell membrane bilayers. It can be transformed into phosphatidylcholine, but it nevertheless has its own roles in the cell. This phospholipid aids in the assembly of membrane proteins and without it they may not function properly. It may be needed to orient enzymes correctly in the inner membrane.
Phosphatidylinositol is present in all tissues and cell types. It is especially abundant in brain tissue, where it can make up as much as 10% of the phospholipids.There is usually less phosphatidylinositol in tissues than there is phosphatidylcholine, phosphatidylethanolamine or phosphatidylserine, which is to say that it is a minor phospholipid constituent of cell membranes. In cell membranes, it is usually located on the inner side. Phosphatidylinositol is the primary source of the arachidonic acid required for biosynthesis of eicosanoids, including prostaglandins. Derivatives of this phospholipid serve as messenger molecules with the nervous system.
Phosphatidylserine has an affi nity for the proteins found within the cellular membrane matrix. PS is most concentrated in the cells of the brain and nerves. PS promotes the stability and the integrity of the cellular membrane and it promotes the ability of cells to maintain that internal balance known as homeostasis.Nerve cells are particularly dependent upon the actions of the enzymes known as the ATPase’s. Fully 70% of the energy used by the brain and nerve cells may be required simply to maintain the sodium/potassium and the calcium/magnesium balances within these cells. The enzymatic “pumps” literally operate all the time. With age, the activity of these pumps declines, as does nerve function. PS reverses this decline to a certain extent, thus returning membrane functions to a point that more closely resembles that of youth.
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