Metabolism USMLE Step 1 Practice Question

A 50-year-old male was admitted into the hospital of a leading research university with a diagnosis of hepatitis and early cirrhosis of the liver. His past medical history is significant for heavy smoking and only occasional consumption of alcohol. He did not use any drugs, and he had no viral infections. DNA studies showed that he was homozygous for the Z allele of α1-antitrypsin, which introduces a missense mutation producing the improper folding of the protein. A liver biopsy would most likely show accumulation of a proteinaceous substance in which of the following subcellular sites?