Tetrahydrofolates vs SAM

[PDsquash83]

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On Pg 101 of FA 2009, what is the difference between a
1-carbon unit and CH3 groups?

Is it implying that SAM can transfer multiple methyl groups while tetrahydrofolate can only do one carbon?

Thanks,

 

[haloschief]

Bump, I wanted to know if anyone can comment on the importance of SAM? Are vitamins b12 or folic acid required for its functioning/regeneration?

 

[DeeJay2728]

-CH3 IS a one carbon group.

In order to "activate" the CH3-THF we get from our diet we must take its methyl group off (-CH3). We do this by giving the methyl group to Homocysteine (via Homocysteine methyltransferase aka Methionine synthase) but this happens ONLY if B12 is present (B12 is a cofactor for the enz and B12 transfers the methyl group as methylcobalamin). Once Homocysteine gets methylated, it becomes Methionine.
Now we have to regenerate Homocysteine, so we can "activate" some more folate. In order to do this Methionine has to give the methyl group to someone else, that's when SAM comes in. SAM takes the methyl group from Methionine, so Methionine can become Homocystine and start this process over.
I like to think of the -CH3 group as a Hot Potato.

 

[dyspareunia]

-CH3 IS a one carbon group.

In order to "activate" the CH3-THF we get from our diet we must take its methyl group off (-CH3). We do this by giving the methyl group to Homocysteine (via Homocysteine methyltransferase aka Methionine synthase) but this happens ONLY if B12 is present (B12 is a cofactor for the enz and B12 transfers the methyl group as methylcobalamin). Once Homocysteine gets methylated, it becomes Methionine.
Now we have to regenerate Homocysteine, so we can "activate" some more folate. In order to do this Methionine has to give the methyl group to someone else, that's when SAM comes in. SAM takes the methyl group from Methionine, so Methionine can become Homocystine and start this process over.
I like to think of the -CH3 group as a Hot Potato.

SAM doesn't "take the methyl group from methionine". ATP and Methionine join to form SAM. Then SAM methylates something (like NE to form Epi) and becomes S-Adenosine, which is reconverted into homocyst[e]ine (not homocystine) and adenosine.

 

[lp430]

SAM doesn't "take the methyl group from methionine". ATP and Methionine join to form SAM. Then SAM methylates something (like NE to form Epi) and becomes S-Adenosine, which is reconverted into homocyst[e]ine (not homocystine) and adenosine.

SAM = S-Adenosyl Methionine

I didn't realize that for the longest time. Makes more sense now.

 

[DeeJay2728]

You're right SAM doesn't "take the methyl group". In order to generate SAM you need ATP and Methionine. This is how SAM has the ability to "donate/transfer a methyl group", in other reactions. Sorry about the spelling... Homocyst[e]ine.

 

[wonderkin]

On Pg 101 of FA 2009, what is the difference between a
1-carbon unit and CH3 groups?

Is it implying that SAM can transfer multiple methyl groups while tetrahydrofolate can only do one carbon?

Thanks,

To answer the original question: the difference is that CH3 has to be CH3 for for SAM, where tetrahydrofolate can be a CH3 or other single carbon groups like -CH2, -COH etc. So tetrahydrofolate is a little more flexible, while SAM is more specific.