Vitamin C deficiency impairs collagen maturation even though the amino acid sequence of procollagen is normal. The immediate biochemical failure is best explained by which mechanism?

• A Loss of ferrous iron in prolyl and lysyl hydroxylases, halting hydroxylation of procollagen ✓
• B Failure of lysyl oxidase to oxidatively deaminate lysine residues
• C Impaired cleavage of terminal propeptides by N- and C-procollagen peptidases
• D Defective glycosylation of hydroxylysine residues in the Golgi apparatus

Explanation

Prolyl and lysyl hydroxylases require molecular oxygen, alpha-ketoglutarate, and ferrous iron. During catalysis iron is oxidized to the ferric form, and ascorbate acts as the reducing agent that regenerates Fe2+. Without vitamin C the enzymes are inactivated, hydroxylation stops, and the triple helix becomes unstable at body temperature because hydrogen bonds dependent on hydroxyproline cannot form. Lysyl oxidase needs copper, not ascorbate, and peptidase cleavage is unaffected, eliminating the other options.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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