B6 Flashcards
B6 2 functions and excess
process AA
lower homocysteine levels
First B vit to have adverse effects w excess
B6 main coenzyme form
PLP main coenzyme and main transport in plasma
needs FMN(riboflavin) to convert other forms to PLP
function 1 B6
transamination: ALT: alanine aminotransferase heart, liver, muscle
reversible amino group transferred
alanine + aKG = pyruvate + glutamate
3 reactions in TCA
pyruvate + PLP = alanine
aKG + PLP = glutamate
oxaloacetate + PLP = aspartate
energy from protein or dispensible aa
2 function of B6
synthesis of heme
need for protoporphyrin from glycine + succinyl CoA + PLP = heme
protoporphyrin + Fe = heme
anemia that looks like Fe deficiency in B6 deficiency, not common
function 3 of B6
TRP to niacin conversion
kynureninase needs PLP
if no PLP/def = xanthurenic acid build up *abnormal metabolite
function 4 of B6
Synthesis of Cysteine from MET via Homocysteine
methionine -> homocysteine + cystathionine synthase (w PLP) -> + cystathionine lyase (wPLP)==== cysteine
B6 role in HCY levels
MET donates methyl via SAM and becomes HCY = cysteine
HCY increases if PLP reactions that convert HCY to other products/cysteine have reduced activity bc of B6 deficiency
*directly involved to decrease levels of HCY
B6 food sources
protein
whole grains, B6 can be added
meat and alts
milk products
plants not well utilized: DRIs assume mixed diet
RDA of B6
1.3mg
assess status of B6
measure plasma PLP
B6 deficiency
clinical: not common bc of adequate protein
self prescribing can lead to excess intake
B6 clinical conditions of deficiency
alcohol: also deficiency risk for other B vits
inhibits conversion of pyridoxine and pyridoxamine to PLP
drugs: isoniazid
tuberculosis
interferes with vit activity
symptoms of B6 def
microcytic anemia= decrease synth of heme, not a common cause of anemia
dermatitis
convulsions: decrease neurotransmitter GABA
depression and confusion: decrease serotonin and dopamine
nerve damage: impaired myelin sheath formation
CV: hyperhomocysteinemia controversial
functional test of B6
2g TRP
TRP -> niacin won’t happen bc PLP enzyme kynureninase can’t convert so xanthurenic acid urine build up
B6 toxicity and UL
UL = 100mg from food and supplements
peripheral sensory neuropathy: first B vit to be shown as toxic
symptoms: tingling, burning pains, clumsiness, ataxia, numbness in limbs
reversible
