vit B6

Question 1

what forms can vit B 6 be found in

Answer 1

pyridoxine
(plants & supplements)

pyridoxal(animal sources)
pyridoxamine

all also exist in phosphorylated form

Question 2

vit B6 kinase and phosphatase reactions

Answer 2

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

Question 3

what is PLP

Answer 3

cofactor in amino acid metabolism and of glycogen phosphorylase

Question 4

what is the Noncoenzyme role in regulating actions of steroids

Answer 4

Binds to lysine on steroid receptors to reduce binding of steroid hormones e.g oestrogen; testosterone; cortisol

So, diminish action of steroids

Question 5

what is the excretory metabolite

Answer 5

4-pyridoxic acid
(< 30 µm/d = deficiency)

Question 6

recent intake of 4-pyridoxic acid is in what

Answer 6

urine

Question 7

plasma PLP measurement values for deficiency and adequate intakes

Answer 7

< 20 nmol/l = deficiency
> 30 nmol/l = adequacy

Question 8

what converts pyridoxal to 4-pyridoxic acid

Answer 8

aldehyde oxidase

Question 9

what are the value requirements of vit B6 in relation to amino acid metabolism
EAR=
RNI=

Answer 9

EAR = 13 ug/g protein
RNI = 15 ug/g protein

Question 10

what is the RNI for vit B6 for males and for females

Answer 10

RNI male 1.4 mg/d
RNI female1.2 mg/d

Question 11

diets high in what can cause vit B6 deficiency

Answer 11

protein

Question 12

name some good sources of vit B6

Answer 12

meat – steak; salmon; chicken; liver; whole grain products;

Vegetables; some fruits e.g. bananas; nuts; egg yolk; yeast

Question 13

what percentage of vit B6 is lost in refining cereals

Answer 13

90 %

Question 14

what are symptoms of vit B6 deficiency

Answer 14

fatigue, glossitis, stomatitis, anaemia, hyperhomocysteinaemia

convulsions (infants – severe heat treatment of milk)

Question 15

what groups are at risk of vit B6 deficiency

Answer 15

elderly, alcoholics, certain drug therapies (e.g. isoniazid, anti-convulsants, corticosteroids), asthmatics (theophylline).

Question 16

describe toxicity in terms of vit B 6

Answer 16

high doses advocated in certain medical conditions e.g. carpal tunnel syndrome; nausea & vomiting in pregnancy (maximum 200 mg/day)

Question 17

high doses of vit B6 are used in treatment for what

Answer 17

tuberculosis (maximum 200 mg/d)

Question 18

pyridoxine at high levels causes what

Answer 18

neurotoxicity