A biochemistry student calculates the ATP yield from complete oxidation of an odd-chain fatty acid. The final round of beta-oxidation produces one acetyl-CoA and one three-carbon intermediate. Before entering the TCA cycle, this intermediate must first be converted to succinyl-CoA through a pathway requiring:

• A Vitamin B12 as a coenzyme for methylmalonyl-CoA mutase
• B Folate-dependent one-carbon transfer
• C Biotin-dependent carboxylation followed by vitamin B12-dependent rearrangement ✓
• D Pyridoxal phosphate-dependent transamination

Explanation

Propionyl-CoA from odd-chain fatty acids is carboxylated by biotin-dependent propionyl-CoA carboxylase to D-methylmalonyl-CoA, racemized, then rearranged by C12-dependent methylmalonyl-CoA mutase to succinyl-CoA. Option A describes only the second half of the pathway and omits the obligatory initial carboxylation, so it is incomplete. This same pathway catabolizes valine, isoleucine, methionine, and threonine.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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