Cobalamin Flashcards
What are the 2 active coenzymes that our bodies can convert B12 into?
5-deoxyadenosylcobalamin
Methylcobalamin (CH3)
What is the main B12 formed by microorganisms?
Cyanocobalamin
Cyanocobalamin is found in what sources?
It’s the form in vitamins and added to cereals
What does B12 from blue-green algae (spirulina) produce mostly, and what is it’s metabolic effects?
Pseudovitamin B12. Not active in humans
Intrinsic factor is secreted from what, where?
Parietal cells of the stomach
How is Vitamin B12 digested and absorbed?
See slide 228
What conditions can decrease vitamin B12 digestion & absorption?
Zollinger-Ellison syndrome (too much HCl)
Medications for GERD (not enough HCl)
Pancreatic insufficiency (not enough proteases to release B12 from R proteins)
Malabsorptive syndromes
50% of B12 is absorbed where?
Ileum
B12+IF is released where and becomes what?
Enterocyte, becomes B12
After the enterocyte, where does B12 go and how?
To the liver bound to transcobalamins in blood
After the liver where does B12 go?
Leaves liver bound to transcobalamins in blood, then goes to be stored in bone, liver (50% storage here), brain, muscles.
What significant compound and function is made as a product of the coenzymatic function of methylcobalamin
As methylcobalamin turns into cobalamin, homocysteine turns to methionine, which then turns into SAMe, an important factor in myelination
What is the B12 coenzyme called and what does it mediate?
Adenosylcobalamin. Threonine and isoleucine metabolism or metabolism of odd-chain fatty acids.
What is the RDA for B12?
Adults = 2.4 mcg
What are the sources of B12?
Shellfish Meats Poultry Fish Dairy (some lost through pasteurization) Fortified cereals
How much B12 is lost from cooking?
33%
What 2 conditions are associated with B12 deficiency?
Megaloblastic anemia
Pernicious anemia
If you have a B12 deficiency, but you are good on folate, what symptoms of megaloblastic anemia will be taken care of and what ones remain?
Folate can get rid of hematologic symptoms, but not neurologic symptoms due to demyelination of nervers
What is the direct cause of megaloblastic anemia with B12 deficiency?
Decreased DNA synthesis
What is pernicious anemia?
Type of megaloblastic anemia. Autoimmune condition where antibodies attack gastric, parietal and mucosal cells.
What happens with HCl secretion in pernicious anemia?
Decrease in HCl secretion (achlorydia) causes impaired B12 release from food proteins
What happens with IF in pernicious anemia?
Impaired IF secretion causes inability to absorb B12
What is the tx for pernicious anemia?
B12 injections
What is the cause of B12 deficiency, inadequate absorption or intake?
Inadequate absorption
What is the toxicity levels for B12
None
T/F
Vegans will develop B12 deficiency relatively quick
False
May take 5-10 years before deficiency
If you are elderly and 15% deficient, what is the best way to alleviate the problem?
Take IM injection or nasal spray
