Vitamin B6 Flashcards
- _____ soluble
- Discovered in _____ when found to alleviate a dermatitis in rats
- Has both _____-______ and _______ functions
- Characterised by _-_______ ring
- Occurs naturally in _ vitamer forms + phosphorylated compound forms based on
pyridine ring: - pyridoxine (PxN) (alcohol - mainly plants)
- pyridoxal (PxL) (aldehyde - plant/ animal foods)
- pyridoxamine (PxM) (amine - mainly animal foods)
- Water
- 1930s
- energy-releasing, hematopoietic
- N-containing
- 3
- metabolically active form is _______ _______ (PLP)
pyridoxal 5’phosphate
Digestion & Absorption of B6
* B6 vitamers occur in foods mainly as the ________ forms.
Small Intestine
*Phosphate released by _______ _______ in small intestine
*Absorption of mainly ________ form by ______ diffusion in jejunum
*High bioavailability (___-___%)
*______ metabolism in intestinal cells. Most PN, PL & PM released directly into ______ ______
- phosphorylated
- alkaline phosphatase
- unphosphorylated, passive
- 60-90
- Limited
- portal blood
Metabolism & Transport of B6
* _____ takes up and metabolizes most newly absorbed B6
* ___ conversion to ________ forms
* Vitamers mostly converted to ________ ______ (PLP), the active coenzyme form
* Transported in blood mainly as PLP on _______
- Liver
- Rapid, phosphorylated
- pyridoxal phosphate
- albumin
Storage:
* Moderate storage relative to other _-_______
* Body content __-___ mg
* __-__% in muscle, _-__% liver
* Time frame for deficiency about _ _____
- B-vitamins
- 40-185
- 75-80
- 5-10
- 3 months
Excretion:
* Mainly _____ excretion
* With dietary levels
~ 50% as _______ _____, inactive oxidised
breakdown product
~ 50% ________
* With supplements
* mainly excreted __________
- urinary
- pyridoxic acid
- unchanged
- unchanged
Summary of Functions
* As PLP a coenzyme in multiple reactions involving ______ _____ metabolism
* Role in modulation of ______ ______: binds to ___, modulates steroid hormone or transcription factor binding to DNA
- amino acid
- gene expression, DNA
Amino Acid Metabolism Functions 1
* Transamination for synthesis of non-essential AAs
* transfer of NH2 gp from a AA to a keto acid → new AA
* Dehydration/Deamination
* Amino group removed from a compound (e.g. and amino acid) and released as NH3/NH4+
* E.g., removal of amino group from threonine
* Transulfhydration Required for two enzymes needed to synthesize cysteine
from methionine
Amino Acid Metabolism Functions 2
* Decarboxylation Reactions
* Involved removal of COO-
* Synthesis of amine neurotransmitters
* DOPA to dopamine
* tryptophan to serotonin (5 hydroxytryptamine)
* glutamate to GABA (g-aminobutyric acid)
* Synthesis of histamine from histidine
* Transulfhydration PLP required for enzymes needed for cysteine to be synthesized from methionine
* Transelenation similar to sulfur except for seleno amino acids
* Cleavage e.g. methyl group transferred from serine to tetrahydrofolate (THF) to form 5,10 methylene THF (see folate lecture)
* Racemization – Required for racemases that catalyze interconversion of D- and L- amino acids
Amino Acid Metabolism Functions 3
* Coenzyme needed in haem synthesis
* Cofactor needed in sphingolipid synthesis (nerve sheath)
* Coenzyme with kynureninase for conversion of tryptophan to
niacin via kynurenine pathway (see niacin lecture)
* Synthesis of carnitine and taurine
Glycogen Degradation
* PLP occurs in muscle as coenzyme for _______ _______ (glycogen → glucose-1-PO4)
* Helps body release ________ stored as _____ for
use as energy
- glycogen
phosphorylase - carbohydrate, glycogen
Deficiency of B6 - Adults
Symptoms of deficiency:
* general weakness (decrease utilisation of muscle _____)
* depression, insomnia (decrease synthesis ___________)
* increase plasma homocysteine (decrease degradation to ________)
→ increase risk of atherosclerosis (evidence inconsistent) ?
* enhanced sensitivity to ______ _______
→ increase risk hormone sensitive _____? (no strong evidence)
- glycogen
- neurotransmitters
- cystathione
- atherosclerosis
- steroid hormones
- cancer
Deficiency of B6
- Anaemia – A condition in which the amount of _______ in the blood of an individual, or the number of red blood cells, is below the normal range for a healthy population of comparable age & sex.
- Anaemia can result from __ _________ due to the role of B6 in haem formation
- It results in a _______ (small RBC) ________ (deficient pigmentation) type of anaemia. Looks similar to Fe Deficiency Anaemia
- haemoglobin
- B6 deficiency
- microcytic hypochromic
Deficiency of B6 - Children
* Symptoms in children have included _______ (decrease GABA)
* _____ epidemic of convulsions after using high ____-_______ milk formula (B6 → unavailable form pyridoxyl lysine)
* Symptoms also include rash, weakness, fatigue, ______, _______,
angular _______
- convulsions
- 1954
- heat-treated
- cheilosis, glossitis, stomatitis
Risk Groups for B6 Deficiency?
Severe B6 deficiency is _____
* Chronic high ______ intake (80-100%)
* impaired absorption
* ________ from alcohol metabolism displaces PLP from binding to functional proteins →↑PLP catabolism & → ↓ PN & PM → PLP
* Some drugs can ______ or bind to PLP
* E.g. isoniazid (anti-TB), corticosteroids, anticonvulsants
- rare
- alcohol
- acetaldehyde
- inhibit
