B6,B9,B12 Flashcards
Folate B9 folic acid
folate b9 active form body
tetrahydrofolate THF
folate b9 active form food
polyglutamate
folate b9 sources
- Yeast, mushrooms, green vegetables, legumes, liver,
fortified foods, citrus fruits – especially strawberries and
oranges
Folate b9 enzyme that hydolyze it
conjugase
Folate b9 conjugase inhibitor
low zinc status, alcohol, inhibitors in foods
folate b9 function
- Functions in single carbon transfers in:
- Nucleic Acid Synthesis
- dUMP converted to dTMP (required for DNA
synthesis) - Carbon donator in purine synthesis
- Essential for cell division
- Amino Acid Metabolism
- homocysteine converted to methionine
- Glycine converted to serine
resynthesis of methionine from homocysteine
- Methionine -> homocysteine
Too much want to convert back to methionine
-2 ways: either converting to something else
(cystathionine) with use of VitB6 or go back
to methionine w/ methionine synthase
-Too much homocysteine = risk higher CVD
-PLP to help homocysteine to cystathionine
-1 methyl group difference in cystathionine to
become methionine (methylcobalamine)
Methylcobalamin (cobalamin is B12) to
homocysteine
-cobalamin left when become methionine - Cobalamin can get methyl group and
become methylcobalamin from 5-methyl
THF
-Becomes THF = active form of folate - THF becomes 5,10 methylene THF
-1 way direction, trapped in body
*All other forms of folate can convert to each
other as long as it is not in the form of
5,10 methylene THF
-THF used for glycine and serine - Cobalamin B12 saves the trapped form of
folate in body
folate b9 deficiency
Megaloblastic Anemia
* immature red blood cells
* Due to decreased DNA synthesis and improper cell
division along with continued RNA production
folate b9 deficiency risk
- Pregnancy
- Birth defects highly
correlated with folate
deficiency - alcoholism
- Elderly
- Phenytoin users
(anticonvulsant)
folate b9 toxicity
- Supplementation may mask
B12 deficiency while
permitting neurological
damage caused by B12
deficiency - Megadoses may induce
seizures in epileptics - UL: 1 mg/d from
supplements and fortified
foods
Folate b9 interactions
Vitamin B12: Methyl-
folate trap
- Without B12, methyl group
in N5 methyl THF cannot be
removed - Zinc:
- Folate may decrease zinc
absorption - Zinc deficiency may
decrease folate absorption
Folate b9 assesment
- Plasma, serum, or RBC
folate - Deoxyuridine suppression
test (from dUMP to dTMP) - Plasma homocysteine
concentrations
cobalamin b12 sources
nature B12 is made by
microbes (ie. in
rumen and ileum of some
animals), so animal
products are the main
sources (MFP, egg, milk)
cobalamin b12 absorption
Mechanisms:
I. Intrinsic Factor mediated absorption
1) Intrinsic factor (IF, a glycoprotein) is synthesized in
the stomach.
2) B12 combines with r-protein stomach and
travels to small intestine
3) B12 releases R protein and complexes with IF
4) B12-IF is absorbed in the ileum
5) B12 is released once complex is in the enterocyte
cobalamin b12 function
Converts homocysteine to methionine by transfer of methyl
group from folate to homocysteine
- Converts methylmalonyl CoA to succinyl CoA which can be
used in energy metabolism - nucleic acid synthesis -> through
methionine formation and possibly through reduction of
ribonucleotides to deoxyribonucleotides
cobalamin b12 deficiency
megaloblastic anemia
cobalamin b12 deficiency symptoms
- Large immature red blood
cells, neuropathy, increased
mean corpuscular volume
(MCV) - Usually due to decreased
absorption secondary to
lack of IFas opposed to
decreased intake, called
pernicious anemia
cobalamin b12 at risk groups
- Elderly
- Diseases/Surgery of the
ileum - Alcoholic
- Vegans
- Stomach surgery recipients
cobalamin b12 toxicity
none
cobalamin b12 assessment
- Serum B12
- schilling test
- Used to test B12
absorption/presence of
IF - inc plasma homocysteine
✽ Often done in conjunction
with folate assessment
pyridoxine b6 coenzyme
- PL, PM, PN, PLP, PMP, PNP
pyridoxine b6 sources
- Liver, nuts, bananas, legumes, meat, whole grains, salmon, sirloin steak, white meat chicken
how is pyridoxine b6 metabolised to other forms
by phosphatase to most active form PLP
pyridoxine b6 function
1) Amino acid metabolism
▪ Transamination coenzyme (ie. AST/GOT, ALT/GPT)
▪ Decarboxylation (ie. serotonin production)
▪ Transulfhydration/desulfhydration (ie. methionine to
cysteine or cysteine to pyruvate)
▪ Cleavage (ie. serine to glycine in folate metabolism)
2) Heme formation- with b6 and iron and makes red color of blood
3) niacin synthesis
4) Arachidonic acid production from lineoleate
5) Glycogenolysis (glycogen phosphorylase)
pyridoxine b6 effects
coronary heart disease, premenstrual syndrome, and carpal tunnel syndrome
pyridoxine b6 deficiency symptoms
- Lethargy in adult
- Seizures in infants
- hypochromic/microcytic anemia
- Depression
pyridoxine b6 at risk groups
- Breastfed infants of mothers with deficiency
- Elderly
- Alcoholics
- Oral contraceptive users
pyridoxine b6 assessment
- plansme PLP
- trasaminase activity
- tryptophan load- b6 is required to convert to niacin
B1
B2
B3
B5
B6
B7
B9
B12
Thiamin
Riboflavin
Niacin
Pantothenic Acid
Pyridoxine
Biotin
Folate
Cobalamin
