What does the BHMT enzyme do?The BHMT (betaine homocysteine S-methyltransferase) enzyme is mainly found in the liver. It helps cells to convert homocysteine into methionine. Let’s break this down:
- Homocysteine production happens in the methylation cycle and is part of how the body produces methyl groups. High homocysteine levels have links to heart disease and hearing loss.
- Methionine is an amino acid used by the body in a million ways. It is abundant in food sources, and the body can also make it in a couple of ways, including the reaction involving BHMT.
- Betaine is also known as trimethylglycine (TMG).
Trimethylglycine (methyl donor) + homocysteine (hydrogen donor) → dimethylglycine (hydrogen receiver) + methionine (methyl receiver)To sum up: In the liver, the BHMT enzyme methylates homocysteine in order to produce the needed methionine. This not only helps to keep homocysteine at an appropriate level but also produces a vital amino acid (methionine).[ref]
Understanding the role of BHMT in the methylation cycleAs I mentioned above, the BHMT enzyme involves one way that the body converts homocysteine back to methionine. Another way that cells do this is by using the enzyme methionine synthase. Within the methylation cycle, MTHFR gene variants limit methyl groups produced in the folate cycle. This is linked to higher homocysteine levels in some people due to not enough methionine synthase being available to convert homocysteine back to methionine. The BHMT enzyme can step into that gap — but not in people with genetic variants that decrease the enzyme function.
Impacts of decreases in the methylation cycle:Neural tube defects are a type of birth defect that can occur when there are not enough methyl groups available during pregnancy. This is why folic acid is added to prenatal vitamins and some processed foods in many countries. Cancer rates, such as for breast cancer, increase with low folate - either through genetic variants impacting the methylation cycle or through poor diet. Consuming enough folate-rich foods matters a lot. Many of the genetic variants only have links to an increase in the risk of cancer for people who don’t eat enough folate and/or choline.[ref][ref] While the body has a couple of ways of metabolizing homocysteine, BHMT is important here. In the liver, BHMT is responsible for about half of homocysteine metabolism.[ref] High homocysteine is a marker associated with elevated heart disease risk. A number of genetic variants in the methylation cycle genes have links to higher homocysteine levels as well as heart disease.[ref] The increase in risk can be reduced through the right dietary intake of folate and other B-vitamins.[ref]
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