PROBLEM SET 16. Propionyl-CoA and B12 Coenzyme

PROBLEM SET 16. Propionyl-CoA and B12 Coenzyme

Given:

1. Propionyl-CoA is converted to succinyl-CoA
2. B12 Coenzyme is required

At first sight, conversion of propionyl-CoA to succinyl-CoA appears to be straight forward:

1. Write mechanism for carboxylation of propionyl-CoA and predict the product?

2. What problem does this create for the conversion of propionyl-CoA to sucicnyl-CoA?

The structure of vitamin B12  is:

 

 

 

 

 

 

 

 

 

 

 

 

3. What is the coordination number of this transition metal complex?

4. What is the geometry of the complex?

5. Cobalt is a transition metal. It has 27 electrons. Two of the valance electrons occupy the 4s orbital.
Show the distribution of the valance electrons.

6. The 4s electrons are lost first. Show the distribution of the valance electrons of cobaltic ion (Co+3)

7. How do the valance electrons rearrange to allow the transition complex to form?

8. B12 coenzyme is formed by replacing the cyanide ion with an adenosyl reissue. The structure of B12 coenzyme is:

 

 

 

 

 

 

 

 

 

 

 

Show how ATP is used to form B12 enzyme from Vitamin B12.

9. Assume that B12 coenzyme reacts as a free radical. Write a possible mechanism for the B12 coenzyme catalyzed rearrangement of methyl malonyl-CoA to succinyl-CoA.

10. B12 coenzyme catalyzes a number of 1,2-shift reactions. Write a generalized free radical mechanism for this.

11. Show how the simple mechanism you wrote for the previous question works to convert methyl malonyl-CoA to succinyl-CoA.

12. Add the propionyl-CoA reactions to the metabolic map for threonine that you constructed in the last problem set..

Leave a Comment