Pyridoxine Flashcards
What are the three interconvertible forms (vitamers) of Vitamin B6? what structures do they contain?
- Pyridoxal (PL) = aldehyde
- Pyridoxamine (PM) =amine
- Pyridoxine (PN)=alcohol
what are the physcial properties of pyroxidine? what is it also known as?
-water soluble
-unstable in UV, heat and neutral/alkaline solutions
What is the biologically active form of Vitamin B6? what is the structure of it? what are the reactive groups?
Pyridoxal Phosphate (PLP)
-Phosphorylated PL
1) carbonyl group: needed in AA metabolsim
2) Phosphate group: needed for glycogen phosphorylase
PLP is required for over 100 enzyme-catalyzed reactions, primarily involving amino acid metabolism.
What is the function of PNP oxidase? what does it depend on?
An enzyme needed for PNP/PMP conversion into PLP
-FMN-dependent (riboflavin)
What is the primary metabolic function of Pyridoxal Phosphate (PLP)?
Coenzyme for amino acid metabolism
PLP also plays a role in other biochemical processes:
- transamination
-decarboxylation (NT synthesis)
-transulfuration
-deamination
-phosphorylase/protein structure
-Trp metabolism
-heme synthesis
-glycogen breakdown
What is transamination in the context of amino acid metabolism? why is it important?
Transfer of an amino group between amino acids and keto acids
Essential for amino acid synthesis and catabolism
what enzyme is involved in transamination?
aminotransferase
-name of transferase differs based on the amino acid
What is the purpose of AA decarboxylation? Give two examples of decarboxylation reactions involving amino acids.
Production of hormones and neurotransmitters
* Histidine → Histamine
* Tryptophan → Serotonin
Other examples include glutamate to GABA and tyrosine to dopamine & adrenaline.
What role does PLP play in transsulfuration? what other nutrients are needed? why is this important?
Converts homocysteine into cysteine
-B12, folate
This process is important for reducing homocysteine levels, which is crucial for cardiovascular health.
what is the role of pyridoxine in tryptophan metabolism?
Pyridoxine is needed for kynureninase which is a step in nicotinamide synthesis from tryptophan
What is the primary storage form of pyridoxine in the body?
PLP bound to proteins
Main storage sites are muscle (80-90%) and liver (10%).
what is the role of pyridoxine in heme synthesis?
involved in the heme synthetase
-rate limiting step in heme biosynthesis
what is the role of pyridoxine in glycogenolysis?
more than 50% of prtidoxine in our bodies is involved as a coenzyme for glycogen phosphorylase in muscles
-needed for glycogen synthesis
What is the primary excretion product of Vitamin B6?
Pyridoxic acid
It is eliminated in urine.
What are the main dietary sources of Vitamin B6?
Widely distrubuted; highest sources are meat and unprocessed cereal
Animal tissue: PLP and PMP
Plants: PN
Supplements / fortified food: PN
What factors affect the bioavailability of Vitamin B6? what is the difference in bioavailibility between supplements and food?
- Cooking & processing
- Storage
- Supplement absorption
Supplement bioavailibility >90%
food bioavailibility ~75%
Cooking causes 75-90% loss in cereals due to milling, and plant sources have lower bioavailability.
What are some causes of pyridoxine deficiency?
deficiency is rare due to wide distribution
* Malabsorption disorders
* Alcoholism
* Drug interactions
* Increased requirements
Conditional deficiency can occur due to conditions like Crohn’s or celiac disease.
What are the symptoms of pyridoxine deficiency? who is at higher risk?
- Microcytic anemia
- Increased homocysteine
- Ataxia
- Depression
- Dermatitis
At risk:
-poor diet
-alcoholics (acetaldehyde decreases cellular PLP levels and displaces it from proteins)
Other symptoms include convulsions and confusion.
What is the RDA for pyridoxine? what is the UL?
RDA related to protein intake (atleast 1mg)
UL = 100 mg/day
High doses (>500 mg/day) can lead to sensory neuropathy.
What methods can be used to evaluate Vitamin B6 status?
- Plasma PLP levels
- Urinary pyridoxic acid excretion
- Enzyme activity measurements
High levels of xanthurenic & kynurenic acids in urine indicate deficiency.
what occurs with pyridoxine toxicity?
therapeutic effects on PMS / depression with acute toxicity
evidence varies, >50ng/day may be dangerous and result in peripheral sensory neuropathy in cases >500mg
