Difference Between Sphingomyelin and Phosphatidylcholine

The key difference between sphingomyelin and phosphatidylcholine is that sphingomyelin is a type of phosphosphinghoside while phosphatidylcholine is a type of phosphoglyceride.

Sphingomyelin and phosphatidylcholine are two types of phospholipids in biological membranes. Phospholipids are the most abundant lipids that serve as structural components of biological membranes. They are amphiphilic molecules that are commonly known as polar lipids. The first phospholipid was identified in 1847. It was found in the egg yolk of chickens by the French chemist and pharmacist Theodore Nicolas Gobley. He named this phospholipid lecithin (phosphatidylcholine). In the past decade, purified phospholipids have been commercially produced for applications in various fields such as nanotechnology and material science. Phospholipids have three subcategories: phosphoglycerides, phosphoinositides and phosphosphinghosides.

1. Overview and Key Difference
2. What is Sphingomyelin
3. What is Phosphatidylcholine
4. Similarities – Sphingomyelin and Phosphatidylcholine
5. Sphingomyelin vs Phosphatidylcholine in Tabular Form
6. Summary – Sphingomyelin vs Phosphatidylcholine

What is Sphingomyelin?

Sphingomyelin is a type of phosphosphinghoside, which is a type of phospholipids. It can usually be found in animal cell membranes, especially in the myelin sheath that surrounds nerve cell axons. It consists of phosphocholine and ceramide or a phosphoethanolamine head group. Normally, sphingomyelin has a phosphocholine head group, sphingosine, and a fatty acid. It is hydrolyzed by sphingomyelinases. Upon hydrolysis, it yields fatty acid, unsaturated amino alcohol, phosphoric acid, and choline. Sphingomyelin was first isolated by the German chemist Johann L.W. Thudicum in the 1880s. The structure of this molecule was first reported in 1927 as N-acyl sphingosine-1-phosphorylcholine.

Figure 01: Sphingomyelin Synthesis

The sphingomyelin content in mammals ranges from 2 to 15 % in most tissues. The highest concentration is in nerve tissues, red blood cells, and ocular lenses. Sphingomyelin has specific structural and functional roles in the cell. The metabolism of this molecule creates a lot of products that play significant roles in the cell. Sphingomyelin plays a pivotal role in signal transduction and cell apoptosis. Moreover, sphingomyelin is involved in lipid microdomains (lipid raft) that give more rigidity to the plasma membrane. The sphingomyelin accumulation in the spleen, liver, lungs, bone marrow, and brain causes a hereditary disease called Niemann–Pick disease. This is due to the deficiency of the lysosomal enzyme acid sphingomyelinase. This condition causes irreversible nerve damages.

What is Phosphatidylcholine?

Phosphatidylcholine is a type of phosphoglycerides, which are phospholipids. It was the first phospholipid identified in 1847 in the egg yolk of chickens by the French chemist and pharmacist Theodore Nicolas Gobley. Initially, this compound was termed lecithin (phosphatidylcholine). Gobley completely described the chemical structure of lecithin in 1874. Phosphatidylcholine consists of glycerol, fatty acid, phosphoric acid, and choline. Phospholipase D hydrolyzes the phosphatidylcholine to form phosphatidic acid (PA) and releases the soluble choline head group into the cytosol.

Sphingomyelin and Phosphatidylcholine - What is the Difference

Figure 02: Phosphatidylcholine

They are major components of biological membranes. Egg yolks and soya beans are the chief sources of phosphatidylcholine. It is also a major component of pulmonary surfactant. They can transport between membranes within the cell with the help of phosphatidylcholine transfer protein (PCTP). This molecule plays a pivotal role in cell mediated signalling. Moreover, a 2011 research reported phosphatidylcholine (lecithin) association with atherosclerosis. This is due to a deficiency of one enzyme called lecithin cholesterol acyltransferase, which causes premature atherosclerosis. This condition is a hereditary familial condition. Anyhow, lecithin has numerous health benefits; for example, lecithin is recommended for the treatment of dementia and ulcerative colitis.

What are the Similarities Between Sphingomyelin and Phosphatidylcholine?

Sphingomyelin and phosphatidylcholine are phospholipids.
They both have fatty acids, phosphoric acid, and choline groups.
Both are polar lipids.
These have an amphiphilic nature.
They are both present in biological membranes.
Both play a pivotal role in cell signalling.

What is the Difference Between Sphingomyelin and Phosphatidylcholine?

Sphingomyelin is a type of phosphosphinghoside, while phosphatidylcholine is a type of phosphoglyceride. So, this is the key difference between sphingomyelin and phosphatidylcholine. Furthermore, sphingomyelin does not contain glycerol in its structure. In contrast, phosphatidylcholine contains glycerol in its structure.

The following infographic lists the differences between sphingomyelin and phosphatidylcholine in tabular form.

Summary – Sphingomyelin vs Phosphatidylcholine

Phospholipids are key components of all cell membranes. They are divided into three subcategories: phosphoglycerides, phosphoinositides, and phosphosphinghosides. Sphingomyelin and phosphatidylcholine are two types of phospholipids in biological membranes. Sphingomyelin is a type of phosphosphinghoside, while phosphatidylcholine is a type of phosphoglyceride. Thus, this is the summary of the difference between sphingomyelin and phosphatidylcholine.