One-Carbon Pool Flashcards
What amino acids can be degraded to succinyl CoA
Valine, isoleucine, methionine, threonine
What vitamin is required for the conversion of propionyl CoA to methylmalonyl CoA
biotin (B7)
What is the cofactor for methylmalonyl CoA mutase
methylcobalamin (B12)
What are the cofactors for the conversion of homocysteine to methionine
methylcobalamin (B12) and N5 Methyl FH4 with enzyme homocysteine methyltransferase
What is the cofactor for the conversion of homocysteine to Cysteine
Pyridoxal phosphate (B6), with enzymes cystathionine sythase and cystathionase
How is FH4 converted to N5,10 methylene FH4 for recycling
Serine donates a methyl groups; B6 cofactor
What does Betaine do
Alternate 1-carbon donor to homocysteine to convert it to methionine
What is methylmalonic aciduria
Buildup of methylmalonyl CoA from defect in methylmalonyl CoA mutase. Sometimes helped by high doses of B12
How much B12 does the liver store
2-5mg
What binds B12 in the mouth and stomach
R-binder (haptocorrin)
What binds B12 in the duodenum
Intrinsic factor
In what form does B12 circulate in the blood
Transcobalamin complex
Where does passive absorption of B12 take place
1% of B12 is absorbed passively in the small intestine
In what form is tetrahydrofolate absorbed
Deconjugated and reduced (remove glutamates except 1 and add H to nitrogens)
What enzyme reduces folate and what is its cofactor/hydrogen source
Dihydrofolate reductase; NADPH
Why is folate a vitamin
Because humans cannot synthesize the pterin ring
How is a B12 deficiency determined
Elevation in methyl malonyl acid
How does homocysteine differ from cysteine
homocysteine has one extra carbon on its side chain
What is the methyl trap hypothesis
Some macrolytic anemias respond to B12 or folate treatments because they have a build up of N5-methyl FH4, which cannot be oxidized, and requires B12 to be used
What is the role of B7
It carries/transfers CO2 (most oxidized carbon)
What does THF/FH4 do
carries 1-carbon groups in all oxidation states except CO2
What is the role of SAM
it donates active methyl groups
Where are the reductase and conjugate enzymes that process folate for absorption
They are brush border enzymes
Where are the enzymes that reconjugate folate
It is a cellular conjugase
