Metabolism of vitamin B12
In the plasma, about 20% of the absorbed B12 binds to the serum
protein holotranscobalamin (Holo-TC) for transportHolo-TC is the protein that
delivers bound B12 to all cells in the body. The majority of B12 (80%)
circulating in the blood binds to the serum protein haptocorrin and is biologically
unavailable for most cells. The function of haptocorrin remains unknown.
Only two enzymatic reactions are known to be dependant on
B12 in humans, which are the conversion of methylmalonyl-CoA to succinyl-CoA (a
necessary component of the citric acid cycle) and the conversion of homocysteine
to methionine. The latter reaction is accompanied by the conversion of
methyltetrahydrofolate to tetrahydrofolate, which is necessary for efficient
DNA synthesis. Therefore, a deficiency in B12 can impair DNA synthesis.
No comments:
Post a Comment