vit B6 Flashcards
what forms can vit B 6 be found in
pyridoxine
(plants & supplements)
pyridoxal(animal sources)
pyridoxamine
all also exist in phosphorylated form
vit B6 kinase and phosphatase reactions
dephosphorylated by alkaline phosphatase (Zn-dependent) in intestine
absorbed by active transport only in dephosphorlylated state (pyridoxine; pyridoxal & pyridoxamine)
liver converts to pyridoxal phosphate, main form in circulation (90%)
also formed by erythrocytes, and bound to haemoglobin
absorbed into tissues in phosphate-free form (alkaline phosphatase in blood)
oxidase in vitamin B6 metabolism dependent on riboflavin status
what is PLP
cofactor in amino acid metabolism and of glycogen phosphorylase
what is the Noncoenzyme role in regulating actions of steroids
Binds to lysine on steroid receptors to reduce binding of steroid hormones e.g oestrogen; testosterone; cortisol
So, diminish action of steroids
what is the excretory metabolite
4-pyridoxic acid
(< 30 µm/d = deficiency)
recent intake of 4-pyridoxic acid is in what
urine
plasma PLP measurement values for deficiency and adequate intakes
< 20 nmol/l = deficiency
> 30 nmol/l = adequacy
what converts pyridoxal to 4-pyridoxic acid
aldehyde oxidase
what are the value requirements of vit B6 in relation to amino acid metabolism
EAR=
RNI=
EAR = 13 ug/g protein
RNI = 15 ug/g protein
what is the RNI for vit B6 for males and for females
RNI male 1.4 mg/d
RNI female1.2 mg/d
diets high in what can cause vit B6 deficiency
protein
name some good sources of vit B6
meat – steak; salmon; chicken; liver; whole grain products;
Vegetables; some fruits e.g. bananas; nuts; egg yolk; yeast
what percentage of vit B6 is lost in refining cereals
90 %
what are symptoms of vit B6 deficiency
fatigue, glossitis, stomatitis, anaemia, hyperhomocysteinaemia
convulsions (infants – severe heat treatment of milk)
what groups are at risk of vit B6 deficiency
elderly, alcoholics, certain drug therapies (e.g. isoniazid, anti-convulsants, corticosteroids), asthmatics (theophylline).
