Betaine—homocysteine S-methyltransferase

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Betaine-homocysteine S-methyltransferase

Betaine-homocysteine S-methyltransferase (BHMT) is a zinc-containing enzyme that transfers a methyl group from betaine (trimethylglycine) to the amino acid homocysteine. This reaction makes dimethylglycine and methionine, helping link the body's methylation and amino‑acid metabolism.

What it does
- BHMT is a transferase in the one-carbon transferase family.
- It participates in the metabolism of glycine, serine, threonine, and methionine.
- The enzyme’s activity uses a zinc ion at its active site to catalyze the methyl transfer.

Isozymes
- In humans, there are two isozymes: BHMT and BHMT2, each encoded by a separate gene.

Where it acts
- BHMT is most active in the liver and kidney, helping regulate homocysteine levels in the body.

Clinical significance
- Mutations in BHMT can affect homocysteine metabolism. Abnormal homocysteine levels have been linked to vascular disease and have been discussed in relation to autism, schizophrenia, and neural tube defects. Ongoing research aims to clarify these connections.

Summary
- BHMT helps move methyl groups from betaine to homocysteine, producing dimethylglycine and methionine. It’s important for methionine metabolism and methyl donor pathways, with two human isozymes and primary activity in liver and kidney.