Sphingomyelin is a lipid found in cell membranes, consisting of a polar group, sphingosine, and a fatty acid. It plays a role in cell membrane structure, cholesterol distribution, and signal transmission in nerve cells. Disorders related to sphingomyelin production include acanthocytosis and Niemann-Pick disease.
In biology, a sphingomyelin (SPH) is a special type of lipid that makes up most of the fat content of cell membranes. The structure of SPH consists of a polar group, a sphingosine and a fatty acid. The polar group consists of a molecule of phosphoethanolamine or phosphocholine. This is related to sphingosine, which is an amino alcohol molecule with 18 carbon atoms. The fatty acid part of the structure is usually saturated and is directly related to sphingosine.
Most of the lipids that are part of the structure of cell membranes, particularly in human cells, are derived from glycogen. SPH, however, differs from most cell membrane lipids, because it usually consists of the amino acid serine and the fatty acid palmitate. Sphingomyelin synthase, or sphingomyelinase, is the main enzyme responsible for this chemical reaction.
The functions of SPH are not fully understood. These molecules certainly constitute a fundamental element in the structure of cell membranes. SPH and cholesterol are often discovered in high concentrations together in certain regions of the cell membrane, leading to the hypothesis that the metabolism of these two substances may be related. It is possible that SPH plays a role in controlling the distribution of cholesterol within human cells.
Another important function appears to be signal transmission in nerve cells. This is in line with the observation that the myelin sheath, a membrane found around the long end of many neurons, has a chemical composition with a very high sphingomyelin ratio. In addition to the high concentrations found in nervous tissue, sphingomyelin is also a particularly important component of red blood cells and some mammalian eye cells.
Disorders related to sphingomyelin production include acanthocytosis and the rare Niemann-Pick disease. Acanthocytosis is a syndrome in which red blood cells lose their smooth regular shape and become pointed, or have the shape of a star with a large number of dots. These dysfunctional blood cells can be seen where there is an excess production of sphingomyelin in the blood.
Niemann-Pick disease is an inherited disease characterized by a deficiency of the enzyme sphingomyelinase. This causes sphingomyelin to build up in the brain and many other vital organs. When this occurs in infants, it usually causes severe damage to the brain and is in most cases fatal.
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