Midterm 1 (Lecture 4) Flashcards
Vitamin B6
Six related compounds:
-Pyridoxal, pyridoxine, pyridoxamine and their phosphates
- phosphorylated in foods
- phosphate removed by intestinal enzymes before absorption
- taken up by tissues and re phosphorylated
Coenzyme form: pyridoxal phosphate (plp)
Riboflavin is needed to convert vitamin six to its coenzyme form PLP
Vitamin b six metabolic role
Amino acid metabolism: - transamination, de carboxylation, r group interconversion
Aa metabolism involved in many aspects of intermediary metabolism
4 examples to study
Vitamin B six metabolic role example one
Nervous System
- synthesis of neurotransmitters involve PLP dependent enzymes
Example: serotonin, dopamine
Serotonin synthesized from tryptophan
-Vit B six deficiency = neurological problems
Vitamin B six metabolic role example two
Glycogen breakdown
Hormone function
- PLP can bind to steroid hormone receptors- in nucleus
- inhibits binding of hormone - decreases effects
- steroid responsiveness lower in vitamin B six sufficient vs deficient animals
- implications for steroid dependent diseases (could B six supplements help decrease estrogen levels ex - breast cancer)
Vitamin B six metabolic role example three
Glycogen breakdown
- PLP involved in glycogenolysis
- coenzyme for glycogen phosphorylase
- key enzyme in conversion of glycogen to glucose ( could B six improve glycogen conversion and improving human performance)
Vitamin b6 metabolic role example four
Red blood cell formation and function
PLP involved in synthesis of heme protein
- acts as a coenzyme in heme synthesis
- heme is a component of hemoglobin
- it allows RBC to transport oxygen throughout body
IMINE group
PLP binds to the enzyme (physical interaction) as a coenzyme
The link formed between PLP and the enzyme is called an IMINE group
Assessing vitamin b6 status
assessing based off fact that build up of a substrate/metabolite means deficiency of enzyme
TRYPTOPHAN LOAD TEST
- impaired conversion to niacin
- build up of urinary kynurenic acid (derived from Kynureine pathway
- we know Kynureine needs b6 therefore build of this acid means B6 deficiency
METHIONINE LOAD TEST
- PLP dependent step in methionine metabolism
- methionine is converted to homocysteine which then builds up since PLP is needed to convert homocysteine to cysteine
- increased homocysteine
4-PYRIDOXIC ACID
- major urinary metabolism that is ABSENT with vitamin b6 deficiency
Vitamin B6 deficiency
Nervous system symptoms
- irritability, depression, confusion, sleepiness
- 1950,s formula incident ; seizures observed in infants due to manufacturing error of formula destroying B6
- dermatitis
- cheilosis (lip lesions)
- stomatitis ( inflammation of mouth and lips)
SIMILAR TO B2 deficiency BECAUSE We need B2 to make B6
Vitamin B6 requirement
Affected by
- protein intake (more Amino acids eaten means more B6 produced)
- alcoholism
- pregnancy lactation
Vitamin B6 Drug Interactions
- Anti tuberculosis medications
- anti convulsant medications
High doses of vitamin B6 can decrease efficacy of these drugs by forming complexes with them which:
- decreas3s efficacy of the drug
- decreases vitamin B6 status
Vitamin B6 Health and disease
Cardiovascular disease
- relation to homocysteine
- PLP needed for one Hcy pathway
- PLP shuttles Hcy to cysteine
Depression
- PLP dependent neurotransmitter synthesis serotonin
Premenstrual syndrome (PMS)
- vitamin B6 relieves pms (decreases hormone effects)
Vitamin B12
Largest and most complex structure of B vitamins
Cobalt central part of structure (look for Co in centre of structure)
Also called cobalamin
R group
- R = methyl
- R = adensoyl
- R = CN (supplement form)
Vitamin B12 - Absorption
Complicated process
Three phases involved in its absorption dependent on pH :
- gastric phase
- luminal phase
- mucosal phase
Intrinsic Factor
Key to vitamin B12 absorption
Glycoprotein released into stomach by parietal cells (decrease with age)
Binds vitamin B12
Allows passage into the ileum - ileum has receptor for IF vitamin B12 complex (in final phase)
Absorption than occurs in the ileum
