Betaine-homocysteine S-methyltransferase

Betaine-homocysteine S-methyltransferase

Betaine-homocysteine S-methyltransferase (BHMT) is an enzyme that plays a crucial role in the metabolism of homocysteine, an amino acid that is a key intermediate in the methionine cycle. BHMT catalyzes the transfer of a methyl group from betaine to homocysteine, resulting in the formation of methionine and dimethylglycine. This reaction is important for maintaining homocysteine levels within a normal range and for the regeneration of methionine, which is essential for various biological processes.

Function

BHMT is primarily found in the liver and kidney tissues, where it contributes to the remethylation of homocysteine. The enzyme's activity is crucial for the conversion of homocysteine to methionine, thereby preventing the accumulation of homocysteine, which is associated with cardiovascular diseases and other health issues.

The reaction catalyzed by BHMT is as follows:

Betaine + Homocysteine → Dimethylglycine + Methionine

This reaction is part of the methionine cycle, which is interconnected with the folate cycle and the transsulfuration pathway.

Clinical Significance

Elevated levels of homocysteine, a condition known as hyperhomocysteinemia, have been linked to an increased risk of cardiovascular diseases, stroke, and other health problems. BHMT, by facilitating the conversion of homocysteine to methionine, helps to regulate homocysteine levels in the body.

Genetic variations in the BHMT gene can affect the enzyme's activity and have been studied in relation to cardiovascular risk factors. Additionally, dietary intake of betaine, found in foods such as spinach, beets, and whole grains, can influence BHMT activity and homocysteine levels.

Structure

BHMT is a zinc-dependent enzyme that functions as a homotetramer. Each subunit of the enzyme binds a zinc ion, which is essential for its catalytic activity. The enzyme's structure allows it to bind both betaine and homocysteine, facilitating the transfer of the methyl group.

Also see

• Methionine cycle
• Homocysteine
• Betaine
• Cardiovascular disease
• Folate cycle

External links

• BHMT gene information at NCBI
• PDB entry for BHMT