1. Name two transport proteins in blood for vitamin B12 - which is storage? Which binds more B12 and in what percentage? WHich is the only functional source for B12 uptake?
2. Describe uptake of B12?
3. What happens after B12 is taken up into cells?
1. Transcobalamin I (TCI) - storage form, turns B12 over very slowly ~75% of B12 is bound to this form; TCII - only functional source for B12 uptake.
- 2. TCII-B12 complex is taken up by receptor-mediated endocytosis (pinocytosis)
- 3. Lysosomes free B12 from complex and it immediately binds to methionine synthase or methylmalonyl CoA mutase