Vit B6 B12 Flashcards
is Vit B6 phosphorylated or unphosphorylated in foods
phosphorylated
what is the coenzyme form of Vitamin B6
pyridoxal Phosphate (PLP)
what vitamin is needed to convert pyridoxine to PLP
riboflavin
what are the metabolic role of Vit B6
Amino acid metabolism nervous system hormone function glycogen breakdown red blood cell formation and function immune function
describe the metabolic role of Vit B6
- transamination
- R-group interconversion
- decarboxylations
- recall typrotphan metabolism… synthesis of niacin…kynurenine pathway
Schiff Base
allows PLP to effectively facilitate amino acids metabolism
PLP binds to enzyme
link formed between PLP aldehyde group and enzyme amino group, forms an IMINE group
Vit B6 in nervous system
- synthesis of neurotransmitters involvve PLP-dependent enzymes
- serotonin is synthesized from tryptophan
- Vit B6 deficiency… neurological problems
Vit B6 in hormone function
- PLP is not a hormone but can bind to steroid hormone receptors
- competes with the hormone, inhibits binding and makes it less effective
- could be useful in blocking hormones that are related to diseases
vit B6 in glycogen breakdown
- PLP involved in glycolysis
- coenzyme for glycogen phosphorylase
- key enzyme in conversion of glycogen to glucose
vit B6 in red blood cell formation and function
PLP involved in synthesis of heme
- acts as coenzyme
- allows RBC to transport oxygen throughout body
Pyridoxal (PL) and PLP are able to bind to hemoglobin molecule
affect its ability to pick up and release oxygen
impact on normal oxygen delivery to tissues is not known
B6 in immune function
one carbon metabolism/transfer of one carbon units
serine OH-methyltranferase
synthesis of nucleic acids
assessing Vit B6 statis
Load tests (tryptophan and methionine)
4-pyridoxic acid
tryptophan load test
- impaired conversion to niacin
- build up of urinary kynurenic acid xanthurenic acid; metabolites derived from kynurenine pathway
methionine load test
- 2 PLP-dependent steps in MET metabolism
- methionine–> homocysteine–> cysteine impaired
- increased homocysteins
need B6 to go from homocysteine to cysteine so if B6 is impaired, there will be a build up of homocysteine
assessing Vit B6 status:
4-pyridoxic acid
- major urinary metabolite
- absent with deficiency
B6 deficiency
b6 deficiencies are not usually specific
- nervous system (irritability, depression, confusion, sleeplessness, abnormal EEG patterns)
- dermatitis; cheilosis, stomatitis
- similar to riboflavin deficiency
why is a B6 deficiency similar to a riboflavin deficiency?
if there is a B6 problem, we could have a problem with riboflavin, since we need B6 to convert riboflavin to its coenzyme form
Vit B6 requirement
- requirement affected by protein intake
- oral contraceptives
- alcoholism
- increase in pregnancy and lactation
B6/drug interactions
- anti-TB meds
- anti-consultant meds
- high doses of B6 can decrease efficacy of these drugs
- need to pay attention to balance
- form complexes with Vit B6, reducing the efficacy of drug and creating a vit B6 deficiency
B6 health/disease
- CVD
- relation to homocysteine (Hcy)
- PLP needed for one Hcy pathways
- immune function
- association between low B6 and impaired immune function, especially in elderly
- congnitive function
- role in neurotransmitters
- depression
- PLP-dependent NT serotonin
PMS
-vit B6 used to relieve PMS
OCA side effects (oral contraceptive)
which B vitamin is the largest and most complex structure
B12
cobalmin
what does Vit B12 have in the center of its structure
cobalt
study reminder
need to recognize B12 structure
B12 absorption
- involves 3 phases
- stepwise process that depends on pH and presence of receptors
what are the 3 phases of B12 absorption
gastric phase (stomach) luminal phase (SI) mucosal phase (LI)
Intrinsic factor (IF)
key to B12 absorption glycoprotein release into stomach by parietal cells binds to B12 allows passage into the ileum ileum has receptor for IF-B12 absorption occurs
gastric phase of B12 absorption
- digestion of protein bound B12 (cobalamin)
- free-cobalamin now binds with R-proteins
- IF is synthesized and released by partietal cells but does not bind cobalamin at this point
Luminal phase of B12 absorption
-R-proteins are digested adn free cobalamin again, and can now combine with IF
mucosal phase of B12 absorption
Receptors for IF-B12 complex in the ileum…absorption occurs
what are the two coenzyme forms of B12
methyl cobalamin
adenosyl cobalamin
what is the role of methyl cobalamin
- methionine synthetase
- methionine synthesis
- Hcy to methionine
- also needs folate
what is the rols of adenosyl cobalamin
methylmalonyl CoA mutase
- propionate catabolism
- propionate to methlmalonyl CoA to succinyl CoA
- entry to TCA cycle
B12 malabsorption
atrophic gastritis
- dec gastric acid
- age related decrease in parietal cells that secrete HCl therefore less acid
deacreased intrinsic factor
-age related
pancreatic insufficiency
-decreased protein digestion
B12 deficiency
elevated urinary concentrations of homocysteine and methylmalonic acid
pernicious anemia (changes to red blood cells)
- lack of IF; lack of absorption
- diagnosed with Schilling test…cobalt would be labelled
neurological problems
-slow onset
what effect does folate have on a vitamin B12 deficiency
it masks it.
It can rectify anemia of B12 deficiency but not neurological symptoms
what could you measure that would specifically tell you there is a B12 deficiency
methylmolonyl CoA
food sources of B12
animal products only (meat, dairy, fish)
