## Vitamin C as a Cofactor **Key Point:** Vitamin C (ascorbic acid) is an essential cofactor for hydroxylase enzymes, particularly prolyl hydroxylase and lysyl hydroxylase, which catalyze hydroxylation of proline and lysine residues in collagen. ### Mechanism of Action Vitamin C serves as a reducing agent (electron donor) that: 1. Maintains iron (Fe²⁺) in the ferrous state within the active site of hydroxylases 2. Prevents oxidation of Fe²⁺ to Fe³⁺, which would inactivate the enzyme 3. Enables the hydroxylation reactions essential for collagen cross-linking and stability ### Other Critical Functions | Function | Enzyme/Process | Clinical Significance | | --- | --- | --- | | Collagen stabilization | Prolyl/lysyl hydroxylase | Deficiency → scurvy (defective collagen) | | Carnitine synthesis | γ-Butyrobetaine hydroxylase | Energy metabolism | | Catecholamine synthesis | Dopamine β-hydroxylase | Neurotransmitter production | | Iron absorption | Ferric reductase | Enhances Fe³⁺ → Fe²⁺ reduction | **High-Yield:** Vitamin C deficiency impairs hydroxylation → defective collagen → bleeding gums, poor wound healing, petechiae (hallmarks of scurvy). **Clinical Pearl:** Vitamin C is also a potent antioxidant that regenerates other antioxidants (e.g., vitamin E) from their oxidized forms. [cite:Lehninger Principles of Biochemistry Ch 8]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.