A 24-year-old male from rural Maharashtra presents with progressive tremor, dysarthria, and behavioral changes over 6 months. On examination, slit-lamp examination reveals golden-brown rings at the periphery of the cornea in the Descemet membrane, as marked **D** in the diagram. His serum ceruloplasmin is 12 mg/dL (normal >20 mg/dL) and 24-hour urine copper is 180 mcg/24h. Which of the following is the PRIMARY pathophysiologic mechanism responsible for the deposition of copper in the structure marked **D**?