3115 Folate/ B12
Terms in this set (37)
oxidized form of folate, only 1 glutamic acid residues
reduced form of folate, 2-10 glutamic acid residues
Function of Folate
acceptance/transfer of 1-carbon units in synthesis, interconversion, and modification of nucleotides, amino acids, and other components
Pteridine, para-aminobenzoic acid, glutamic acid
components of Folate
coenzyme form of Folate
5,10- methyl THF
2 main forms of folate found in food
folypoly gamma-glutamyl carboxypeptidase (FGCP)
conjugases (all synonyms)
removes glutamates from folate
duodenum and upper jejunum
location of absorption of folate
monoglutamate (folic acid)
5-methyl tetrahydrofolate (folate)
what forms are absorbed during digestion
Proton Coupled Folate Transporter (PCFT)
what transporter absorbs folate
adding glutamates trap folate
how is folate kept inside cells?
regulatory organ for folate
10-formyl THF (folic acid)
folate is transported in blood in what forms
Free not bound
in the blood what proteins are the forms of folate bound to?
B12 is a coenzyme in the conversion of homocysteine to methionine for the metionine synthetase which catalyzes this reaction. B12 recieves a methyl from 5-methyl THF forming THF
Without B12 5-methyl THF cannot be converted to THF.
Excess folate can bypass this "methyl trap" through interactions with serine to glycine degradation. serine hydroxymethyltransferase catalyzes this reaction
And choline to betaine to glycine.
These interactions can form either 5,10 methyl THF or THF depending on which direction is needed. no need for 5-methyl THF intermediate
Describe methyl trap and the bypassing of it with folate.
reduces homocysteine levels which cannot be converted due to lack of B12
why is betaine an important intermediate of the methyl trap bypassing?
it is a methyl donor during the normal reaction sequence. from methionine to homocysteine
B12's catalyses homocysteine directly to methionione
Describe S-adenosyl methionine's role in methionine to homocysteine
inhibits enzyme dihydrofolate reductase that converts DHF to THF.
This reduces the division of cells
Describe Methotrexate function
Cobalamin (b12 base)
generic term for a group of compounds called corrinoids with a corrin nucleus
corrin nucleus is a macrocyclic ring made up of four reduced pyrrole rings fused together
components of cobalamin
coenzyme form of B12
microoganisms in the gut of animals can synthesize cobalamins
Why is B12 only found in foods?
1) pepsin/stomach acid releases B12 from food
2) B12 binds to an R protein(TC II) in the intestine
3) in the duodenum pancreatic bile release B12 from the R protein and megalin help B12 binds to an intrinsic factor(IF)
4) amnionless B12/IF complex bind to cubulin and is absorbed in terminal ileum through endocytosis
4 step digestion of B12
Transcobalamin I - storage
TC II - digestion (R protein)
TC III - bring back to liver
What are the R proteins for B12 digestion/ functions
protein helps bind B12 to IF
helps cubulin bind to membrane
cubulin (sometimes call itrinsic factor factor)
receptors in the ileum that bind to the B12/IF complex to absorb it
stomach acid is not strong enough to release B12
take mass action supplement and absorb enough through diffusion
why do the elderly have problems with digesting B12? how to get over this?
L-methylmalonyl-Coa is converted to succinyl-CoA.
This is catabolyzed by methylmalonyl-CoA mutase.
B12 is a coenzyme for that enzyme
B12's role in L-methylmalonyl-CoA oxidation
damage to CNS myelinated neurons
only excreted in bile (barely excreted)
binds to blood
N-acetyl paraminobenzoyl glutamate in the urine.
RDA 400 DFE/day
UL = 1mg/day
Folate RDA/AI? UL?
RDA 2.4 micrograms/day
UL = none
B12 RDA/AI? UL?
Dietary folate equivalent
Folate = 1 microgram
Folic acid with food = .6 microgram
Folic acid supplement = .5 microgram
What is a DFE
iron is microcytic anemia not megaloblastic
difference between iron deficiency and folate deficiency?
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