Phosphatidylethanolamine N-methyltransferase

Phosphatidylethanolamine N-methyltransferase

Phosphatidylethanolamine N-methyltransferase (PEMT) is an enzyme that plays a crucial role in the phospholipid metabolism within the liver. It is responsible for the conversion of phosphatidylethanolamine (PE) to phosphatidylcholine (PC) through a series of methylation reactions. This process is essential for maintaining the proper balance of phospholipids in cellular membranes.

Function

PEMT catalyzes the methylation of phosphatidylethanolamine to form phosphatidylcholine. This reaction occurs in three steps, with each step adding a methyl group to the ethanolamine moiety of PE. The methyl groups are donated by S-adenosylmethionine (SAM), which is converted to S-adenosylhomocysteine (SAH) in the process. The overall reaction can be summarized as follows:

PE + 3 SAM → PC + 3 SAH

This pathway is particularly important in the liver, where it provides an alternative route for the synthesis of phosphatidylcholine, complementing the CDP-choline pathway.

Location

PEMT is predominantly found in the endoplasmic reticulum and the mitochondria-associated membranes of liver cells. Its activity is crucial for the proper functioning of these organelles, as phosphatidylcholine is a major component of their membranes.

Regulation

The activity of PEMT is regulated by various factors, including dietary intake of choline, hormonal signals, and the overall metabolic state of the liver. For instance, a diet deficient in choline can upregulate PEMT activity to compensate for the reduced availability of choline-derived phosphatidylcholine.

Clinical Significance

Mutations or deficiencies in the PEMT gene can lead to disorders in phospholipid metabolism, which may result in liver diseases such as non-alcoholic fatty liver disease (NAFLD) and hepatic steatosis. Additionally, altered PEMT activity has been implicated in conditions like cardiovascular disease and metabolic syndrome.

See Also

• Phosphatidylcholine
• Phosphatidylethanolamine
• S-adenosylmethionine
• Liver
• Phospholipid metabolism