Which vitamin acts as a cofactor for carboxylation reactions in metabolism?

Study for the Biochemistry Module 6 Exam. Study with flashcards and multiple choice questions; each question includes hints and explanations. Gear up to ace your test!

Carboxylation reactions rely on a small helper that carries CO2 and hands it off to substrates. That role is fulfilled by biotin, which becomes a prosthetic group on several carboxylase enzymes. Biotin binds covalently to a lysine in the enzyme, and its reactive carboxyl group accepts CO2 to form carboxybiotin. The enzyme then transfers this CO2 to the target molecule, using ATP to activate the CO2 for transfer. This mechanism is central to key metabolic processes like gluconeogenesis (pyruvate carboxylase converting pyruvate to oxaloacetate) and fatty acid synthesis (acetyl-CoA carboxylase forming malonyl-CoA), as well as other carboxylations in propionate and leucine metabolism. Other vitamins mentioned play different roles: thiamine helps with decarboxylation and aldehyde transfers, while niacin and riboflavin function as redox cofactors in dehy­drogenase reactions, not as carboxylation carriers.