Vitamin B6 Flashcards
INFO
B6 - grp of 3 pyridine derivatives - pyridoxine , pyridoxamine , pyridoxal
active coenzyme form - pyridoxal phophate (PLP)
about 40% of plp is present in the muscles combined with phosphorylase
FUNCTIONS OF COENZYME
PLP mainly involved in amino acid metabolism
1. Transamination :- plp acts as coenzymes for transaminases / aminotransferases
2.Decarboxylation :-
decarboxylation of all AA require PLP as their coenzyme
1)histidine → histamine
2) 5-hydroxy tryptophan → serotonin
3) serine→ ethanolamine
4)cysteine → taurine
5)glutamate → GABA
3.Glycogenolysis - 1st step utilises plp as coenzyme
DEFICIENCY MANIFESTATIONS
—-NEUROLOGICAL
—-DERMATOLOGICAL
—-HEMATOLOGICAL
1.NEUROLOGICAL MANIFESTATIONS :- most common
B6 def. → enzymes of NS function poorly
↓
↓ serotonin , epinephrine , GABA , noradrenaline
↓GABA → causes convulsions in children
plp – involved in sphingomyelin formation
B6 def.→ demyelination of neuron and peripheral neuritis
2.DERMATOLOGICAL
↓B6 → ↓TRYPTOPHAN → ↓NIACIN →PELLAGRA
3.HEMATOLOGICAL :-
causes hypochromic microcytic anemia due to impaired heme biosynthesis
impaired antibody formation also takes place
VitB6 therapy affects other disorders- xanthuranic acidura and homocystinura
ASSAY
assay by activating erythrocytic transaminases by adding PLP into reaction mixture
Recent – radioimmunoassay (direct estimation)
EFFECT OF DRUGS
1.isonicotinin acid hydrazide (isoniazide{INH})
anti-tuberculosis drug, inhibits pyridoxal kinase →↓plp
2.cycloserine -
women taking oral contraceptive pills have mild vitB6 def.
3. ethanol -
converted into acetaldehyde in our body wihch inactivates plp
SOURCES AND RDA
Rich sources - fish,egg,milk,oil seeds,whole cereals , legumes , green leafy vegetables , yeast , polishing rice
RDA
adults :- 2-3mg/day
preganancy and lactation :- 3mg/day
TOXICITY
intake>100mg/day – sensory neuropathy
further excess – numbness muscle weakness nerve damage imbalance
