Question
Methylmalonyl aciduria is seen in deficiency of‑
| A. | Vitamin B12 |
| B. | Vitamin B6 |
| C. |
Vitamin C |
| D. |
Folic acid |
|
Correct Answer � A Explanation |
 |
Ans.A. Vitamin B12
Propionate is a major precursor of glucose in ruminants. It enters gluconeogenesis via the citric acid cycle.
After esterification with CoA, propionyl-CoA is carboxylated to D-methylmalonyl-CoA, catalyzed by propionyl-CoA carboxylase, a biotin-dependent enzyme.
Methylmalonyl-CoA racemase catalyzes the conversion of Dmethylmalonyl-CoA to L-methylmalonyl-CoA, which then undergoes isomerization to succinyl-CoA catalyzed by methylmalonyl-CoA mutase.
In nonruminants, including human beings, propionate arises from the β-oxidation of odd-chain fatty acids that occur in ruminant lipid as well as the oxidation of isoleucine and the side chain of cholesterol and is a (relatively minor) substrate for gluconeogenesis.
Methylmalonyl-CoA mutase is a vitamin B12 -dependent enzyme and in deficiency of this vitamin methylmalonic acid is excreted in the urine (methylmalonic aciduria).