A 30-year-old woman presents with hepatic cirrhosis, Kayser-Fleischer rings and neuropsychiatric symptoms. Serum ceruloplasmin is low. In Wilson's disease, the defective protein ATP7B normally functions to:
- A Incorporate copper into ceruloplasmin and excrete copper into bile in hepatocytes ✓
- B Transport dietary copper from enterocytes to portal blood
- C Bind free copper in serum, preventing oxidative damage
- D Mediate renal copper reabsorption in proximal tubules
Explanation
ATP7B is a P-type copper-transporting ATPase located in the trans-Golgi network of hepatocytes. It performs two critical functions: (1) it incorporates copper into apo-ceruloplasmin to form holo-ceruloplasmin in the Golgi, and (2) it traffics to the canalicular membrane under copper-overload conditions to excrete excess copper into bile. In Wilson's disease, defective ATP7B causes failure of both biliary copper excretion (leading to hepatic copper accumulation) and ceruloplasmin copper incorporation (low serum ceruloplasmin). Copper overflows into blood and deposits in brain, cornea and kidneys. ATP7A (Menkes disease protein) transports copper in enterocytes and other tissues except liver. Ceruloplasmin itself binds copper but is not responsible for copper excretion.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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