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Role of B12 and Folate in the Conversion of Homocysteine to Methionine

fbirder profile image

I thought I would summarise the role of B12 and folate in the conversion of homocysteine to methionine.

As you can see in the diagram, methylcobalamin plays no special role. It, like other forms of B12, is converted to cob(II)alamin as soon as it enters the cell. For this reaction the cob(II)alamin is further reduced to cob(I)alamin. It is this that binds with the enzyme =,

A molecule of methylfolate and a molecule of homocysteine also bind with the enzyme. A methyl group is passed from the methylfolate to the cob(I)alamin which then passes it on to the homocysteine, converting it into methionine.

So methylcobalamin is formed, but fleetingly.

It should also be clear that taking methylcobalamin if you have a faulty MTHFR enzyme would be pointless.

11 Replies
Gambit62 profile image

Should first sentence in second para be 'methylcobalamin plays no special role' rather than 'methylfolate plays no special role'?

fbirder profile image
fbirder in reply to Gambit62

Thanks. Edited.

Thanks for that fbirder . I can’t say that I understand it all , but I’ve printed it out and will give it great attention . I had my homocysteine tested before I started self-injecting B12 (Hydroxocobalamin ) and supplementing with folic acid , and it was 15 . After a few months of weekly injections I was pleased to see it was 7 .Unfortunately an expensive test , so I won’t be doing it again in a hurry .

Want to say that when I told my doctor about the two results , she said it was no use telling her , as she knew nothing about homocysteine readings . I couldn’t believe it .

fbirder profile image
fbirder in reply to wedgewood

Yes, it's a shame there isn't a better test available. It seems to me that routine testing could catch a lot of problems before they manifest.

Foggyme profile image

Thanks for this fbirder. Very useful indeed.

Any objections if I pin the post so that it's easily accessible in the future?

fbirder profile image
fbirder in reply to Foggyme

Nema problema

Foggyme profile image
FoggymeAdministrator in reply to fbirder

Thanks fbirder. Fairly new post so will leave open for a week (ish) then turn off replying ...or else you'll be responding to replies for, well...possibly decades 😳.

Thanks, fbirder, that's excellent!

Thanks very much, fbirder.

If you take (or inject) methyl B12, what happens to the methyl group that is removed?

fbirder profile image
fbirder in reply to Martin_12

I don’t know.

There are lots of other biochemical reaction that will remove methyl groups. I suspect it will initially be removed as methanol which would then get further oxidised to formate and then to carbon dioxide. CH3-O-H -> O=CH-O-H -> O=C=O

Methanol is fairly common in the human body. It’s only dangerous in very high amounts (grams rather than micrograms). Here’s some info

i love the science you post.

helps me feel empowered to understand the biological process

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