Scurvy

A 56-year-old man with a history of alcohol use disorder and social isolation presents with fatigue, easy bruising, joint pain, and poor wound healing for three months. He subsists primarily on processed foods and canned soups with no fresh fruits or vegetables for over a year. On examination, he has marked gingival hypertrophy with bleeding gums, corkscrew hairs, and the characteristic skin findings marked as **C** in the diagram—perifollicular hemorrhages with hyperkeratosis on the thighs, buttocks, and arms. Serum ascorbic acid is markedly low at 0.08 mg/dL (normal 0.4–1.5). What is the primary biochemical mechanism underlying the skin and hemorrhagic manifestations seen at **C**?