Question

The enzyme Propionyl CoA carboxylase which helps conversion of Propionate to Succinyl CoA needs the following as a coenzyme

• A. Vitamin B12
• B. Biotin
• C. Thiamine
• D. Riboflavin

Hint:

Remember the "ABC" rule for carboxylases:
ATP, Biotin, and Carbon dioxide ($CO_2$) are required by almost all carboxylase enzymes.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Odd-chain fatty acids, certain amino acids (valine, isoleucine, threonine, methionine), and cholesterol side chains are degraded to yield propionyl-CoA.
Propionyl-CoA must be converted into the citric acid cycle intermediate succinyl-CoA through a three-step pathway.

Step 2: Detailed Explanation:
The pathway converting propionyl-CoA to succinyl-CoA is as follows:
Propionyl-CoA is carboxylated to D-methylmalonyl-CoA by the enzyme propionyl-CoA carboxylase.
D-methylmalonyl-CoA is epimerized to L-methylmalonyl-CoA by methylmalonyl-CoA epimerase.
L-methylmalonyl-CoA is isomerized to succinyl-CoA by the enzyme methylmalonyl-CoA mutase.
Propionyl-CoA carboxylase belongs to the family of carboxylase enzymes that catalyze the addition of a carboxyl group (from $HCO_3^{-}$) to a substrate.
Almost all carboxylases (such as pyruvate carboxylase, acetyl-CoA carboxylase, and propionyl-CoA carboxylase) require biotin (Vitamin B7) as an essential coenzyme.
Biotin is covalently attached to a lysine residue of the enzyme and acts as a carrier of activated carbon dioxide.
While the final step of this pathway (catalyzed by methylmalonyl-CoA mutase) requires cobalamin (Vitamin B12) as a coenzyme, the carboxylation step catalyzed by propionyl-CoA carboxylase relies strictly on biotin.

Step 3: Final Answer:
The coenzyme required by propionyl-CoA carboxylase is biotin.