Review Note

Vitamin B12 Physiology:
1. Vitamin B12 is also known as ______
2. Describe the structure of Vitamin B12
3. What two forms are found in foods?
4. What two forms are found in co-enzymes?
5. Vitamin B12 is important in two pathways:
    a. Conversion of ______ CoA to ______ CoA by ______ CoA mutase which requires co-enzyme form of vit B12 (______). In B12 deficiency, ______ accumulates which is used as diagnostic test in megaloblastic anemia. 
    b. Transfer of one methyl group from ______ to ______ to generate methionine by the enzyme ______ which requires vit B12 (______) as coenzyme. This reaction is the link between vit B12 and folate.

1. Vitamin B12 is also known as Cobalamin
2. It is a tetrapyrrole ring with cobalt in the middle attached to a ribonucleotide (5,6-dimethylbenzimidazolyl)

3. Hydroxy-cobalamin and cyano-cobalamin
4. Methyl-cobalamin and 5′-deoxyadenosylcobalamin 
5. Vitamin B12 is important in two pathways:
                                     
    a. Conversion of methylmalonyl CoA to  CoA by succinyl CoA mutase which requires co-enzyme form of vit B12 (5’-deoxyadenosylcobalamin). In B12 deficiency, MMA (methylmalonic acid) accumulates which is used as diagnostic test in megaloblastic anemia. 
    b. Transfer of one methyl group from 5-methyl THF to homocysteine to generate methionine by the enzyme methionine synthase which requires vit B12 (methylcobalamin form) as coenzyme. This reaction is the link between vit B12 and folate.