Propose a method to study the effect of protein disulfide isomerase deficiency on protein folding in the ER.

• A. Compare glycosylation patterns in wild-type and protein disulfide isomerase-deficient cells.
• B. Measure the rate of GTP hydrolysis in cells lacking protein disulfide isomerase.
• C. Use a cell line with a knocked-out protein disulfide isomerase gene and analyze protein folding and stability.
• D. Assess the localization of proteins in cells with and without protein disulfide isomerase.

Answer: (C)