Biotin (vitamin B7) serves as a CO2 carrier in carboxylation reactions. Biotin deficiency (or biotinidase deficiency) impairs which set of clinically important enzymes?

• A Pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and branched-chain alpha-keto acid dehydrogenase
• B Methionine synthase, methylmalonyl-CoA mutase, and homocysteine methyltransferase
• C Pyruvate carboxylase, acetyl-CoA carboxylase, propionyl-CoA carboxylase, and 3-methylcrotonyl-CoA carboxylase ✓
• D Transketolase, transaldolase, and glucose-6-phosphate dehydrogenase

Explanation

Biotin is covalently attached to specific lysine residues of four mammalian carboxylases: (1) pyruvate carboxylase (pyruvate → OAA, gluconeogenesis); (2) acetyl-CoA carboxylase (acetyl-CoA → malonyl-CoA, fatty acid synthesis); (3) propionyl-CoA carboxylase (propionyl-CoA → methylmalonyl-CoA, odd-chain FA and branched AA catabolism); and (4) 3-methylcrotonyl-CoA carboxylase (leucine catabolism). Biotinidase deficiency impairs biotin recycling from dietary protein and from enzyme turnover, causing organic acidaemia, rash, alopecia, and metabolic acidosis. The dehydrogenases use lipoic acid, thiamine (TPP), FAD, NAD+, and CoA. Methionine synthase and methylmalonyl-CoA mutase use cobalamin. Transketolase uses thiamine.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.