Folate and B12 Metabolism Flashcards
What is the most oxidized form of folate?
N10-formyl-THF
What is the most reduced form of folate?
N5-methyl-THF
What folate rxn is catalyzed by Serine Hydorxymethyltransferase?
THF to N5N10 methylene THF
What is the most common form of folate found in the circulation?
N5-methyl-THF
What enzymatic rxn keeps folate inside the cell?
addition of polyglutamate
What form of folate is required for the production of serine from glycine? Produced?
THF
produced = N5N10-methylene THF
What form of folate is required for methionine synthase?
N5-methyl-THF
produced = THF
What form of folate is required for thymidylate synthase? Produced?
required = N5N10-methylene-THF
produced = dihydrofolate
What form of folate is required for purine synthesis?
N10-formyl-THF
produced = THF
What form of folate is required for histidine metabolism? Produced?
required = THF
produced = N5-formamino-THF
What rxn does Thymidylate Synthase catalyze?
dUMP to dTMP
What are the four forms of cobalamin?
cyanocobalamin
hydroxycobalamin
adenosylcobalamin
methylcobalamin
What is B12 complexed to in order for reuptake into cells to function?
transcobalamin
What type of cell produces transcobalamin?
ileal mucosa
In what organelle is B12/TC degraded?
lysosome
What protein is the majority of B12 complexed to in the circulation?
Haptocorrin
Which form of cobalamin is B12?
cyanocobalamin
What two forms of cobalamin must cyanocobalamin be converted into in order to function within the cell?
adenosylcobalamin
methylcobalamin
How much of the radioactive form of B12 should a patient without a B12 deficiency urinate out during a negative Schilling Test?
at least 7%
Will patients with an IF deficient have an abnormal Part 1 or Part 2 Schilling test?
Part 1
What four amino acids get shunted into methylmalonyl-CoA?
Thr, Ill, Met, val
What type of fatty acids get shunted through methylmalonic-CoA?
odd-chain
Which cofactor is required for carboxylation of propionyl-CoA?
biotin
Which form of cobalamin is required for converion of methylmalonyl-CoA to succinyl-CoA?
adenosylcobalamin
Which form of cobalamin is required for the conversion of homocysteine to methionine?
methylcobalamin
What rxn is the ONLY reaction that can regenerate THF from N5-methyl-THF?
methionine synthase
What type of fatty acids will be accumulated into myelin during a B12 deficiency?
odd-chain
What is the most common cause of acute megaloblastic anemia?
NO inhalation
What form of cobalamin does nitrous oxide destroy?
methylcobalamin
What two rxn’s are catalyzed by Dihydrofolate Reductase?
folate to dihydrofolate
dihydrofolate to tetrahydrofolate
The folate receptor has the highest affinity for what form of folate?
N5-methyl-Folate
What forms of folate are used during the activity of Methionine Synthase?
N5-Methyl to THF
Folate receptors have the highest affinity for what form of folate?
monoglutamate
Dietary folate contains what amino acid? How are these connected?
glutamate
polyglutamate
What form of THF is found in the diet? Circulation?
diet = polyglutamate
circulation = monoglutamate
In the portal blood, B12 is found complexed to what protein?
transcobalamin
